Discussion: View Thread

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Dr. Prevatt I have used this dialogue to help focus my HOA Board of Directors in their deliberations to raise speed limit within our gated community from 30 MPH to 35 MPH – I also raised the issue of liability i.e. speed limit set by builder developer prior to turn-over – Richard W. Goodwin PhD PE Consulting Engineer Lake Worth FL 5/16/17

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

I certainly am not one to advocate for adding lanes and higher speeds to all roads.  Many roads were built along cart or wagon ways where a straight line between two markets was shorter than a path a few days out of the way.  Now, that shorter road provides only a few minutes difference - 20 miles was then a day's travel, now less than half an hour.  Combining that with federal money spent paving roads that have almost nothing to do with interstate commerce and we have many rural roads that are indeed a waste of taxpayer money.  Efficient travel means, for most, the furthest distance in the least time.  Setting the speed limit at the 85th percentile on an interstate with a mildly further distance will further decrease the traffic on smaller, local roads that may be a bit shorter in miles, decreasing the speed differential on both - providing more efficient travel for the vast majority, and safer travel on the less used roads for e.g. bicyclists, as the local tax base provides.  

The insinuation that we should be slowing travel on interstate or other highways to a speed where bicyclists would feel comfortable occupying the driving lane, or introducing obstacles to decrease the efficiency of commuting or transporting goods, seems to be less than a realistic viewpoint.

 

Dr. Prevatt I have used this dialogue to help focus my HOA Board of Directors in their deliberations to raise speed limit within our gated community from 30 MPH to 35 MPH – I also raised the issue of liability i.e. speed limit set by builder developer prior to turn-over – Richard W. Goodwin PhD PE Consulting Engineer Lake Worth FL 5/16/17

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

I certainly am not one to advocate for adding lanes and higher speeds to all roads.  Many roads were built along cart or wagon ways where a straight line between two markets was shorter than a path a few days out of the way.  Now, that shorter road provides only a few minutes difference - 20 miles was then a day's travel, now less than half an hour.  Combining that with federal money spent paving roads that have almost nothing to do with interstate commerce and we have many rural roads that are indeed a waste of taxpayer money.  Efficient travel means, for most, the furthest distance in the least time.  Setting the speed limit at the 85th percentile on an interstate with a mildly further distance will further decrease the traffic on smaller, local roads that may be a bit shorter in miles, decreasing the speed differential on both - providing more efficient travel for the vast majority, and safer travel on the less used roads for e.g. bicyclists, as the local tax base provides.  

The insinuation that we should be slowing travel on interstate or other highways to a speed where bicyclists would feel comfortable occupying the driving lane, or introducing obstacles to decrease the efficiency of commuting or transporting goods, seems to be less than a realistic viewpoint.

 

Dr. Prevatt I have used this dialogue to help focus my HOA Board of Directors in their deliberations to raise speed limit within our gated community from 30 MPH to 35 MPH – I also raised the issue of liability i.e. speed limit set by builder developer prior to turn-over – Richard W. Goodwin PhD PE Consulting Engineer Lake Worth FL 5/16/17

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Definitely a subjective analysis. One should consider the complexity of modern life - e.g. there is not a single person on Earth who can make a pencil all by oneself. If one does not need pencils etc. then certainly roads are too big. Another applicable mathematical concept is the "limit." Consider the quality of life if one could not even cross the road (errhh path) to trade. Making us all geographic prisoners is not the answer, and that is the true result of following the irrational concept of "induced demand."

When considering civilization one cannot ignore reality in analyses. Certainly reducing lane widths to reduce the 85th percentile speed would improve safety, all other things being equal. However, all other things are not equal.

Again, I certainly agree that there are overbuilt roads in the US that are based on cart paths from hundreds of years ago, and federal dollars spent improving roads with questionable interstate commerce relevance may not be the best use of federal tax dollars, but those dollars are non sequitur to the question of following the logic of the 85th percentile speed limit.

Further, even the concept itself of a speed limit on interstates may not be rational if we are to follow the Constitution. Consider the Montana Paradox for example, or the safety record on the Autobahn. That, however, is beyond the scope of this subject line.

I certainly am not one to advocate for adding lanes and higher speeds to all roads.  Many roads were built along cart or wagon ways where a straight line between two markets was shorter than a path a few days out of the way.  Now, that shorter road provides only a few minutes difference - 20 miles was then a day's travel, now less than half an hour.  Combining that with federal money spent paving roads that have almost nothing to do with interstate commerce and we have many rural roads that are indeed a waste of taxpayer money.  Efficient travel means, for most, the furthest distance in the least time.  Setting the speed limit at the 85th percentile on an interstate with a mildly further distance will further decrease the traffic on smaller, local roads that may be a bit shorter in miles, decreasing the speed differential on both - providing more efficient travel for the vast majority, and safer travel on the less used roads for e.g. bicyclists, as the local tax base provides.  

The insinuation that we should be slowing travel on interstate or other highways to a speed where bicyclists would feel comfortable occupying the driving lane, or introducing obstacles to decrease the efficiency of commuting or transporting goods, seems to be less than a realistic viewpoint.

 

Dr. Prevatt I have used this dialogue to help focus my HOA Board of Directors in their deliberations to raise speed limit within our gated community from 30 MPH to 35 MPH – I also raised the issue of liability i.e. speed limit set by builder developer prior to turn-over – Richard W. Goodwin PhD PE Consulting Engineer Lake Worth FL 5/16/17

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?

Despite my skepticism of literature published by the Cato Institute, I read the article linked above. I did not find the author's argument compelling.

I do agree that modern life is complex, and I'm glad that it is. Complexity correlates well with resiliency. Far from supporting or facilitating complexity, highways lead to simplification and homogeneity. Simplification, in turn, reduces the resiliency of our communities.

Were highways used solely to move freight and trade, the argument that they expand markets and enrich modern life might be more compelling, though certainly not unassailable. But highways are not congested because of freight. They are congested because of elective trips and routine commutes that have followed from our auto-centric development since WWII. Highways are certainly not the only cause of this development pattern, but they are an integral part of it.

It is confusing to me when intelligent people go to such great lengths to defend the mode of transportation that has proven to be one of–if not the–most expensive, most dangerous, least energy efficient, and most environmentally and socially destructive options available to us. Incremental mitigation of some of these shortcomings does not strike me as worthwhile when dramatically better options are already widely available. That private automobiles give the illusion of freedom and independence does not justify the enormous externalized costs required. A return to designing our built environment for people rather than for a single overused tool is long overdue.

I've been browsing the roads portion of ASCE's Infrastructure Report Card this morning. There is every likelihood that I'm overlooking something, but it would appear that the ASCE is calling for expenditures on highways that are far greater than the money they suggest such expenditures would save in time, fuel, damage to cars, safety improvements, &c. That could be part and parcel of a major problem in this country and culture: the dominance of the automobile is taken for granted in the design of our built environment rather than subjected to a clearheaded evaluation on its merits.

As counterpoint to Cato's attitude and the article above, consider Ivan Illich's work, Energy and Equity. Regardless of whether one agrees with all (or any) of it, Illich's approach to evaluating technology in Energy and Equity is worth examining.

Definitely a subjective analysis. One should consider the complexity of modern life - e.g. there is not a single person on Earth who can make a pencil all by oneself. If one does not need pencils etc. then certainly roads are too big. Another applicable mathematical concept is the "limit." Consider the quality of life if one could not even cross the road (errhh path) to trade. Making us all geographic prisoners is not the answer, and that is the true result of following the irrational concept of "induced demand."

When considering civilization one cannot ignore reality in analyses. Certainly reducing lane widths to reduce the 85th percentile speed would improve safety, all other things being equal. However, all other things are not equal.

Again, I certainly agree that there are overbuilt roads in the US that are based on cart paths from hundreds of years ago, and federal dollars spent improving roads with questionable interstate commerce relevance may not be the best use of federal tax dollars, but those dollars are non sequitur to the question of following the logic of the 85th percentile speed limit.

Further, even the concept itself of a speed limit on interstates may not be rational if we are to follow the Constitution. Consider the Montana Paradox for example, or the safety record on the Autobahn. That, however, is beyond the scope of this subject line.

I certainly am not one to advocate for adding lanes and higher speeds to all roads.  Many roads were built along cart or wagon ways where a straight line between two markets was shorter than a path a few days out of the way.  Now, that shorter road provides only a few minutes difference - 20 miles was then a day's travel, now less than half an hour.  Combining that with federal money spent paving roads that have almost nothing to do with interstate commerce and we have many rural roads that are indeed a waste of taxpayer money.  Efficient travel means, for most, the furthest distance in the least time.  Setting the speed limit at the 85th percentile on an interstate with a mildly further distance will further decrease the traffic on smaller, local roads that may be a bit shorter in miles, decreasing the speed differential on both - providing more efficient travel for the vast majority, and safer travel on the less used roads for e.g. bicyclists, as the local tax base provides.  

The insinuation that we should be slowing travel on interstate or other highways to a speed where bicyclists would feel comfortable occupying the driving lane, or introducing obstacles to decrease the efficiency of commuting or transporting goods, seems to be less than a realistic viewpoint.

 

Dr. Prevatt I have used this dialogue to help focus my HOA Board of Directors in their deliberations to raise speed limit within our gated community from 30 MPH to 35 MPH – I also raised the issue of liability i.e. speed limit set by builder developer prior to turn-over – Richard W. Goodwin PhD PE Consulting Engineer Lake Worth FL 5/16/17

Stephen Hemphill wrote:

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.


Expanding markets may well expand an economy, but you may be conflating road-building with expanding markets. In some cases, building a road would expand a market. In other cases, building or expanding a road would disperse a market without expanding it, thereby decreasing the efficiency of an existing market. Even if we assume that building a road does expand a market, the expansion might not be enough to generate revenue adequate to fund building or maintaining that road. In such a case, the road is not economically advantageous.

This is the situation we are in and have been for some time. All the really economically advantageous roads--the roads that did expand markets enough to cover their construction and maintenance--were built long ago. It is economically rational to allocate resources to the maintenance of those roads, though probably not their expansion. Instead, we continue to build and expand roads that lead directly to more dispersed development and do not generate enough revenue to cover their cost if they generate any revenue at all. These roads, instead of building our economy, drag it down.

There are clearly problems in cities. Efficiency of infrastructure compared to suburban and rural areas is not one of them. We are all welcome to live in an outer ring suburb or in the rural hinterland, but please don't ask others to subsidize the ever-expanding highway system required to travel at unlimited speed from that suburb to a productive city at any time of the day. And lest it be suggested that without an enormous interstate highway system we would be unable to receive a widget from across the continent in a timely manner, well, I suppose I have no problem with that suggestion. I do take issue with the premise that it rests on: that effectively instantaneous delivery of goods from anywhere at all has value surpassing the costs it requires. It does not.


Stephen Hemphill wrote:

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

How high would such a tax rise? Can you assume an inelastic demand for fuel as taxes on it increase? As the after-tax price of fuel increases, would not the demand fall, requiring a further tax increase, and on and on? If wear on roads is proportional to the 4th power of axle weight, should that be the basis of fuel taxation? Should elective trips with no social value beyond that to the driver be taxed on the same basis as freight or emergency vehicles? What of electric vehicles that may be quite heavy but consume no liquid fuel?

I would not vote against a dramatic fuel tax increase, but I also do not believe it would ever raise enough revenue to maintain our current road system, much less pay for expanding it.

Stephen Hemphill wrote:

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

I might add that doing away with the bicycle path altogether and instead designing streets that can safely be shared by all users would be an even more efficient use of limited resources.

Other examples of inappropriately-applied standards include designing large rights-of-way "for safety" that then lead to an 85th percentile speed that is unsafe for non-motorized users everywhere and even motorized users at intersections. Such a right-of-way would also diminish the usefulness of a street for any economic productivity. Again, I believe that the 85th percentile speed is better used to determine good road or street design based on a desired safe speed for all users and productive uses than to determine the appropriate speed limit of an existing street or road following a speed study.

While I agree that increasing the percentage of taxes is generally not favorable, one must remember that increasing the tax base by increasing productivity and salaries or wages "increases taxes" too.  For some a historical reminder is in order.  A couple of generations ago (e.g.) Los Angeles was in its heyday, as factories were but a few blocks from residents, "Tab A" for a widget was a few blocks in one direction, "Slot B" a few blocks in another direction, spare parts nearby as well.  This led to huge income inequalities, and those in rural areas could not as easily afford to buy widgets.  With the interstate system (and other highways), just in time supply by UPS, FedEx etc., things are changing - although income disparities vs. quality of life are still the norm to some extent, depending of course on one's individual definition of "quality of life."  Add to that decades of throwing primitive solvents and other wastes that we now know more about out the back door and it's no wonder there's a problem convincing people to "infill" to old urban neighborhoods. 

The statement "Contrary to the assertion that roads create productivity, they are an incredible drag on the economy at all levels, from national to local" seems to forget history as well, as it treats the economy as a zero-sum game.  Expanding markets expands the economy, therefore taxes - without a percentage increase on the individual.

I do agree "Engineers should be designing solutions that solve problems instead of creating more problems because that's what the standards promote or because "that's the way it's (always been) done"".  Sometimes use of standards is not within the realm of "engineering" and is just a worst case solution for technicians.  Sometimes use of more modern materials are much cheaper in the long run (aka life cycle costs) as well - a huge example is warm mix asphalt combined with heavy use of SBS.  Not only are there synergistic effects of that combination, but the decrease in relative cost between asphalt and SBS make a considerable difference in life cycle cost as well, discounting the validity of the old "PG" grading system which was developed when that difference was high.  Bicycle paths with much thinner sections, adjacent but not attached to roadways is another good example.

Finally, taxing fuel, while some may consider it a tax increase (rather than just catching up) aligns with the concept of "taxing bads, not goods."  Traffic damage to roadways is approximately proportional to the 4th power of the axle weight.

All of these factors and more combine to reinforce the mathematical truism of the 85th percentile speed, which should not be confused with a "standard."

I would personally prefer the 4 lane roadway a half mile from my home (via pavement) to have a slower speed limit than the 55 mph it has now, all other things being equal so I could more comfortably ride my bicycle on it.  But they are not equal.  Who is going to pay for it?  The tax base considers that the shorter (in time) the commute, the more time we have for a) productivity (aka wages) and b) time with family and friends.  Therefore, I must relegate myself to riding the local 2 lane residential roadways for recreation.  Otherwise, value adding business will less likely be coming to my area, nor will the corollary:  Employment opportunities for all those nearby needing to provide for their families.

It comes down to personal responsibility vs. bias or a feeling of entitlement.  Somebody has to pay for the roads.  With the imminence of globalization productivity is paramount as well.  Commute times and (and yes, distances) need to be minimized, as commuting is the very antithesis of quality of life for the vast majority.  We, as civil engineers, need to remember we are building civilization for the public, not our own personal desires.  The 85th percentile is a mathematical truism.  When one begins to ignore math the system degrades.

"Safely" seems a bit subjective in this case. In my experience, people who request lower speed limits are interested in the safety of all road users, not just those in automobiles. It turns out that 40 mph is not at all safe for those outside the confines of a large metal cage. And no, I do not believe saving a few seconds or even minutes on a commute or an elective trip in an automobile is more important than the safety of pedestrians and cyclists. It would behoove regulators and engineers to remember that roads and streets are public spaces and that optimizing them for one use at the expense of all others can and does lead to inequity along with a host of other negative consequences.

In some ways, limited access highways are a different matter, but not entirely. The conclusions drawn half a century ago by David Solomon and others suggested that speed differentials have greater impact on safety than absolute speed. Those conclusions have recently been called into question, and rightfully so.

Valuing the speed of travel over all else has had, and continues to have, huge negative impacts on our development patterns and our built environment. These, in turn, negatively impact quality of life for a great many people.

The concept of 85th percentile speed could perhaps be re-purposed to more beneficial uses: design streets so that the natural speed is a safe one for all users.

The FHWA has done an admirable job making our highways safer, at the same time vehicles are much safer at speed as well.  Over 50 years ago highways were pretty much a bloodbath, then seatbelts became required as an early step toward improving safety and work has continued very well on that vein.  Back then freeway speeds were limited, typically out west anyway, to 75 mph with some slightly lower.  The "Montana Paradox" here and here showed setting freeway limits below the 85^th percentile had negative effects, but federal dogma (aka "or else lose your funding") forced Montana to reinstitute them.  If anyone has the original study it would be great to see - apparently it is being suppressed. 

Anyway, setting the speed limit at the +1 standard deviation of the free flow speed, or the inflection point of the bell curve, has been widely accepted as the optimal engineering solution.  That is approximately the 85^th percentile, and where traffic "platoons" more.

As a litmus test for where the country is going in terms of becoming more competitive in the world, I am interested if the engineering community is heading toward backing the 85^th percentile concept for freeway speed with the improvements in productivity and safety; or maintaining the speed limits that have been (with the exception of the misguided federal 55 and then 65 mph mandate for a few years) stagnant despite significant engineering advances in both roads and vehicles.  A few states have raised limits to 80 and even 85 on one toll road in Texas, but for the most part it seems the old standards are stuck in place.

Comments?