Pedro,
I would also like to clarify the interpretation of the 4-foot minimum width included in the AASHTO Bike Guide. (Our firm collaborated with AASHTO to write the 2012 guide and is currently working on an update.) The 4-foot dimension is based on the minimum operating space needed by the cyclist and is intended to exclude the gutter pan. This is because the seam between the pavement and the gutter can represent a crash hazard for cyclists. If the curb and gutter are TXDOT standard with a vertical curb, then the distance from the face of curb should actually be 5 feet, 4 inches if possible. A 4-foot width that includes the gutter pan should only be used in "extremely constrained" low-speed roadways (< 45 mph) when no gutter is present (see section 4-13 of the Bike Guide), and should only be used over short distances.
Providing 4 feet outside of the gutter pan also allows the cyclist room to navigate around things like drainage structures. TXDOT standard curb inlets are of particular concern, since the depression in the gutter pan at the curb opening is 4 inches. That is a pretty significant discontinuity in the surface of the bike lane, and also represents a crash hazard for the cyclist. If any of the inlets include grates, then the grates should be replaced with bicycle safe grates prior to adding bike lanes.
If your project includes areas where there is on-street parking, the Bike Guide also recommends a 6-foot width where the bike lane is adjacent to parking. The 6-foot dimension allows additional operating space for cyclists to avoid vehicle doors that may be opened without warning or vehicles that may be maneuvering in and out of perpendicular or diagonal spaces along the roadway. "Dooring" is most common in downtown areas where parking turnover is high, but the potential should be considered anywhere a bike lane is adjacent to parking. If you have the luxury of additional pavement beyond what is needed for the vehicular travel lanes and bike lanes, additional buffering should be considered. Vehicle doors usually extend about 3 feet when opened, so providing a 3-foot buffer or separation between parking and bike lanes is desirable.
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Melany Alliston-Brick, P.E., M.ASCE
Civil Engineering Practice Director, North America
Toole Design Group, LLC
Silver Spring, MD
(571) 830-4272
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Original Message:
Sent: 09-20-2018 16:35
From: Pedro Zavagna
Subject: Bicycle Lanes width
Hello everyone,
I am currently doing the design for a city, where we will be doing some re-striping job on roads where the city has jurisdiction. For this reason, we are following the AASHTO - Guide for the Development of Bicycle Facilities, 2012, where it says a minimum width of 4ft for bicycle lanes.
However, TxDOT is supervising the entire job, and TxDOT has a 5ft minimum width for bicycle lanes guideline.
Should we follow the TxDOT guidelines with the 5ft, or since we are only working with local roads is the 4ft acceptable?
Thanks.
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Pedro Zavagna A.M.ASCE
(903)504-2985
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