Go to www.jamsafety.com to see the SAFTI-TRAX Detectable Warning System for the Visually Impaired. It is currently recommended by the US government for curb ramp delineation and other hazardous pedestrian areas.
I represent the Canadian distributor of Cotel's SAFTI-TRAX Detectable Warning System for the blind and visually impaired. This truncated warning system has been specified by the US government and many DOT's for use on curb ramps.
http://www.jamsafety.com