The 2010 ADA Standards do not require detectable warnings on curb ramps. They are only required at transportation platform boarding edges.
810.5.2 Detectable Warnings. Platform boarding edges not protected by platform screens or guards shall have detectable warnings complying with 705 along the full length of the public use area of the platform.
Requirements for detectable warnings are included in the proposed Guidelines for Public Right-of-Way. Although this document has not yet been adopted, it provides very good guidance for public ROW projects.
Here in Texas, a curb ramp located within a site is no longer required to contrast with adjoining surfaces or include detectable warnings or grooves.
Detectable warnings are required where accessible routes enter hazardous vehicular areas. This cannot be found in the 2012 TAS but is instead hidden away in the Texas Architectural Barriers Administrative Rules. A hazardous vehicular area includes all street crossings but does not include most driveways or pedestrian crossings within a site. Crossings at signalized driveways require detectable warnings.
Keep in mind that detectable warnings are required where are route enters a street even if there is no curb ramp.
The area covered by the detectable warnings should be limited to the 24″ minimum at the curb line. There is no benefit to providing more detectable warnings.