You have probably walked over them thousands of times and not even noticed them, unless you’ve slipped on one: those red, orange and sometimes black, ridged composite tiles stuck in the concrete at almost every sidewalk intersection ramp in Philadelphia and surrounding counties. These two-by-four-foot tiles are known as detectible warning surfaces, or DWS, and are designed to aid the visually impaired in detecting when they have reached the corner of a sidewalk intersecting with a street.
Much like the ramp upon which they sit, the DWS is federally mandated by the Americans with Disabilities Act to be installed whenever construction plans warrant any rebuilding of the sidewalk or curb area. The handicap ramp is in place at every corner to assist individuals in wheelchairs to enter and exit the sidewalk. The ADA mandates the maximum slope of the handicap ramp to ensure that wheelchair users are able to easily enter and exit the sidewalk. That slope is 8.33 percent. The DWS, which is installed in the handicap ramp for the vision-impaired, is necessarily installed at the same slope. If installed at an excessive slope, not only is the purpose of making the sidewalk accessible to those in wheelchairs frustrated, but a pedestrian walking down the handicap ramp on the DWS can have a challenge under certain circumstances.
