Tale of Two Cities

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Keeping up with the ADA, installing curb ramps with detectable warnings.
radiused granite!
Many different ways to install an ADA ramp in terms of workmanship and materials. This photo is from a northern city
which finds economy in using cut radiused granite for its curbs.
asphalt sidewalk
There are doubtless advantages to asphalt sidewalks. They are easier on tree roots? You can make them out of oil? They are cheaper to install? They are better to fall on?
They don’t seem to be durable.
Our town installs these in neighborhoods with a lower socio-economic profile.
30 x10208 px box
G. What are Detectable Warnings, Why are They Required, and Where Must They be Provided?
The ADA Standards require that curb ramps include features called “detectable warnings.” Detectable warnings consist of a series of small domes that contrast in color with the surrounding sidewalk or street. They must be integrated into the walking surface, and there are specific measurements for the size and spacing of the domes.13
What is the function of detectable warnings? Detectable warnings are intended to function much like stop signs for pedestrians who are blind or have low vision. The warnings, which are intended to be felt with pedestrians’ feet, alert blind individuals and those with low vision that they are about to enter a street or other area where cars pass. A detectable warning alerts pedestrians who are blind or have low vision that they need to stop and determine the nature of the hazard – such as whether there is passing traffic – before continuing on their way. 
Under the ADA Standards, curb ramps are required to have detectable warnings that extend the full width and depth of the curb ramp.14 An example of a perpendicular curb ramp that complies with this requirement can be seen to the left. 
The U.S. Department of Transportation (DOT), however, is encouraging the use of a different design for detectable warnings.15 Under this design, detectable warnings extend the whole width of the ramp, but cover only the two feet of the ramp closest to the street. DOT has deemed this departure from the ADA Standards to be permitted under Title II of the ADA.16 An example of a curb ramp that complies with the DOT’s design can be seen on the right.ADA Best Practices