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  • 1.  ADA curb ramps and construction tolerances

    Posted 09-30-2021 03:22 PM

    In Anchorage, we have historically not allowed construction tolerances that would result in exceeding stated maximum cross slopes and running grades of ADA features such as curb ramps in rights of way.  The local construction industry has requested we consider allowing tolerances for cross slope and grade.  Our past position has been that designers should design to less than the maximum, to provide a built-in tolerance.  For example, call out a cross slope of 1.5% to provide a practical 0.5% tolerance during construction.

    However, there is still interest in adopting tolerances that would potentially allow ADA features to exceed 2% cross slope or 1:12 running grade.  I've done some research that shows that jurisdictions are not consistent on this issue.  For example, Seattle appears to allow for tolerances.  Alaska DOT does not.  

    I'd appreciate thoughts/feedback on this issue.  I want to be consistent with federal law, do the right thing for users, and avoid liability for the municipality.

    Thanks -

    Kent Kohlhase P.E., M.ASCE
    Municipal Engineer
    Anchorage, AK

  • 2.  RE: ADA curb ramps and construction tolerances

    Posted 10-01-2021 11:19 AM
    In general, tolerances are not given for cross slopes or grades (whether in ADA ramps or other hard surfaces) because the concrete construction specifications already have tolerances identified, so you if the designer is not careful, the contract could have several tolerances specified for the same item. For the specific issue of the ramps, you need to ask the regulating agency the following hypothetical question: If the project were to be audited after construction and the ramps were found to be non-compliant, but within the tolerance specified, would there be significant corrective action needed? 

    Sergio Fernandez, P.Eng
    Calgary, Alberta,

    Sergio Fernandez M.ASCE
    Senior Transportation Engineer
    Calgary AB

  • 3.  RE: ADA curb ramps and construction tolerances

    Posted 10-04-2021 10:00 AM

    It has been my experience with the Illinois Department of Transportation that no tolerances above the 2% max. cross slope and 1:12 running slope are allowed. As a result, I have incorporated tolerances into my design by keeping the cross slope and running slope below the maximum allowed. This is based on feedback I have received on my designs from coworkers who have been a resident engineer on projects and have been working with the contractors to complete the ADA curb ramps within provided guidelines. The contractors have appreciated having "room" in the field to make the intended design work better in the field. An elevation difference of 0.02' from the survey and field conditions can throw the entire design off. As a result, I generally keep my cross slopes at 1.50% and the running slope at a maximum of 8.0%. I have seen projects that have been audited after construction and replacement required for any curb ramps that were above the maximum 2% cross slope and 1:12 running slope. I hope this helps.

    Jeff Spiller, P.E., M.ASCE
    Project Manager

    Jeffry Spiller P.E., M.ASCE
    Sr Project Engineer
    Maurer Stutz, Inc
    Peoria IL

  • 4.  RE: ADA curb ramps and construction tolerances

    Posted 10-11-2021 10:35 AM

    Hi Kent,
    Excellent question!  I have investigated ADA Ramos in a number of states. Generally, if the ramp is less then the required 1:12 and 2% there is no issue of course. The problems arise when those requirements are exceeded. Those limits were set in place for a reason- safety and maneuverability of the users. My designs are set as a Not To Exceed parameter.  Contractors should easily be able to meet those requirements.  Allowances over the required limits negate those limits in my opinion. If your design is so tight that these critical design features for ADA cannot be easily met then it's possible the design should be re-evaluated.  If the contractors are wanting an allowance for workability- then allow them to reduce the 1:12 and 2% to lesser slopes- that's their tolerance. These are requirements that should be easy enough to meet. If there is difficulty in meeting these maximum limits, that is what should be addressed- why? I don't think allowing a tolerance on an upper limit for an ADA application Is the right thing to do.  "1:10 is close enough" becomes the norm and the ramp is in violation and will be. If ADA does not allow for a tolerance allowing excess, then there should be no allowance above the limit. If they want to construct below the requirements- have at it all day. Our focus is the safe access of ADA users not the comfort and ease of the contractor. 

    Lori Cox, PE
    Principal Engineer

    Lori Cox P.E., M.ASCE
    Principal Engineer
    Houston TX

  • 5.  RE: ADA curb ramps and construction tolerances

    Posted 10-11-2021 10:48 PM
    Rule 1 when there are legal maximums/minimums that must be considered, NEVER design to those numbers.  Take at least the normal tolerances for whatever the construction types and materials involve are and subtract/add as appropriate, as the beginning point.  My preference has always been to use at least double these normal tolerances when defining a dimension.  If any question, increase further.  For example, in passageway widths, think about all the things that may end up being hung on the walls that would constrict the usable width and add allowances accordingly.   If you have a client or owner that insists on using legal maximums/minimums, get this direction clearly stated formally in writing.  Otherwise, if in the normal "what can go wrong will go wrong" reality of construction, the legal requirements are not met, you will probably end up holding the bag.  Use of one-way tolerances, such as +1/4 inch / -0 inch, is somewhat silly, as any contractor worth his salt will probably split the difference for setting out the work.  If the overall ramp height difference is relatively low, think about something like 1:15 or even flatter.

    George Harris Aff.M.ASCE
    Senior Track Engineer
    Olive Branch MS