ADA Intersection Design & Approach Grades

[KevTen]

My question is regarding the design of intersections in steep terrain and meeting all Americans with Disabilities Act (ADA) requirements. I have not seen a great deal of practical documentation regarding real world design of intersections that meet ADA requirements. Some local regulatory agencies have begun to scrutinize the design of intersections in light of ADA. The problem we are having is with the recommendation to “table” intersection so the crosswalk cross slopes do not exceed 2%. For example, suppose you have an 8.0% longitudinal slope on the main street; when you cross the street at the intersection, this 8.0% slope is now the cross slope of the crosswalk; which is “unacceptable”. To avoid this steep sidewalk cross slope, a flat or tabled section of the entire intersection is created. On the main street, ASSHTO guidelines for vertical alignment are followed. However, I can’t find much information regarding allowable design parameters for the stop controlled cross street. For instance, can the cross slope of the main street (2%) and break behind the crosswalk for the approaching street and if so what algebraic difference is allowable. Second, what is a reasonable tangent landing prior to a vertical curve? Third, since this is a stop controlled intersection, what would be an allowable K value? Because it is stop controlled the approach speed is minimal so wouldn’t a lower K value be allowable? Please see the attached a sketch. Any insight would be very helpful and appreciated.

 

[tobeace]

5% maximum grade approaching any intersection, but It doesn't necessarily HAVE to be a tangent, as long as 100' up to intersection is less than 5%. If there is a slight curve less than 100' nobody will care if it's less than 5%.

Yes, I like to break the grade before the cross walk also.

I don't think you need to worry about K as long as you follow the 100' rule, just use whatever K or L req'd in std. regs. L=18A is a good number.



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[TerryScan]

You should check out "Accessible Rights-of-Way: A Design Guide":

http://www.access-board.gov/prowac/guide/PROWGuide.htm

One excerpt: "Alterations must follow the ADA Standards for Accessible Design unless compliance is technically infeasible. Where the nature of an existing facility makes it virtually impossible to comply with all of the accessibility standards applicable to planned alterations, any altered features of the facility that can be made accessible must be made accessible."

One should work with the proper authorities in these situations.

 

[TerryScan]

I just found another document from the access-board site that has a number of examples addressing your issue:

http://www.access-board.gov/prowac/alterations/guide.htm#2

search for "excessive roadway slope". Examples start at page 64 of the PDF verson.