Tactile Warning Truncated Domes

The Americans with Disabilities Act (ADA) Draft Guidelines for Accessible Public Rights-of-Way were revised in November of 2005. The revisions include tactile warning surfaces, also known as truncated domes. A significant difference is the position of the detectable warning on the ramp. Previously, the bottom edge of the 2’ deep detectable warning was to be positioned 6” – 8” from the face of the curb along its entire width. Now the position is to be less than 8” from the face of the curb at one point but does not need to follow the curb line for its entire width. The rest of the leading edge of the detectable warning can be up to 5’ from the face of the curb.

This simplifies the installation of tactile warning surfaces in many cases because it allows the use of a rectangular section of truncated domes. All types of detectable warnings are manufactured this way so that cutting or forming the domes into an angle is no longer necessary.

An additional related revision is the requirement that the grade break of the ramp be perpendicular to the direction of ramp run. The grade break on the vast majority of curb ramps follows the curb line which is rarely perpendicular to the ramp run. This is a fundamental change which will mean that a flat surface or landing will have to be cut into the curb line. This will make the construction of ramps significantly more difficult. The purpose of this revision is to make it easier for wheelchairs to traverse the ramp. Now all four wheels will be in contact with the pavement while previously one wheel would contact the leading edge of the ramp before the other causing the wheelchair to become unbalanced.

It remains to be seen how these revisions will be adopted in the field. The most likely scenario in the short term is that the placement of the detectable warning will be followed while the adjustment of the grade break will not.

By
Bruce Woolner

 

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