Bumps in the road
Whatever the curb design, truncated domes must meet certain standards.
One of the biggest issues that has surfaced in relation to curb ramps is the addition of detectable warnings, which help the visually impaired determine when they are entering a roadway. These warnings initially were required by the Americans with Disabilities Act (ADA) Accessible Guidelines for curb ramps, hazardous vehicular roadways, and transit platform edges.
However, the requirement for curb ramps and vehicular roadways was soon suspended to determine the most effective type of warning.
After 10 years of research, truncated domes proved to be the most viable solution, beating out other options such as grooves, striations, and exposed aggregate.
On July 26, 2001, the suspension on the requirement expired, and truncated domes are now required on all new curb ramps.
Generally, retrofit detectable warning devices are not required for old ramps. However, if a project like street resurfacing is implemented that requires installation of curb ramps, and the existing ramps are otherwise compliant, retrofit detectable warning devices are required.
When installing truncated domes, each curb ramp is unique in its design needs; however, there are certain specifications that are universal regardless of the individual ramp design. All detectable warnings must extend 24 inches in the direction of travel and cover the full width of the curb ramp. Research has shown that this length is sufficient in signaling the beginning of a roadway 90% of the time.
In addition, the warnings must be placed 6 to 8 inches from the curb line to give blind pedestrians enough stopping distance between the curb and the street, and to give wheelchair users a smoother transition from the curb to the street. The domes must be aligned on a square grid so they can be rolled over easily, and each dome has very specific dimensions (best practices indicate 0.9 to 1.4 inches diameter on bottom, top diameter of 50% to 65% of the base diameter, 0.2 inches high, and base-to-base spacing of 1.6 to 2.5 inches from center to center) designed for maximum detectability.New products
Polymer concrete tiles
For curb ramps and crosswalks, the STEP-SAFE skid-resistant tiles are made from a precast polymer concrete matrix that makes them high-strength and resistant to wear, weather, and corrosion. Available in 300 mm squares. Transpo Industries Inc. www.transpo.com..
Ultra-WarningPads are designed with truncated domes to alert the visually impaired to upcoming intersections. The pads come in several sizes and colors, and are made from heavy-duty, flexible urethane material. They install quickly and easily in new construction or as a retrofit. UltraTech International Inc. www.spillcontainment.com..
Armor-Tile detectable warning products come in five styles: cast-in-place, surface-applied, modular pavers, detectable directional, and detectable guidance. These diamond-hard vitrified polymer tiles offer weather and wear resistance. Available in nine colors. Engineered Plastics Inc. www.armor-tile.com..