Where the Sidewalk Ends
Sidewalks with features such as depressed corners, curb ramps, and blended curbs have long accommodated people with limited mobility. But in making these areas safer, we have also made them difficult and even dangerous for the visually impaired to find where the sidewalk ends and the vehicle throughway begins. So, in 1991, when the U.S. DOT and the U.S. Department of Justice developed regulations for new construction and alterations, they included ADA accessibility guidelines (ADAAG), such as installing detectable warning systems, to help ensure safe sidewalks for all.
Dozens of types of detectable warning systems meet ADAAG guidelines. So how does a community determine which to use? State and federal agencies have evaluated different systems for location, installation methods, installation costs, cleaning and maintenance, problems and concerns, durability, and acceptance within a region. In addition, a Vermont study ofdetectable sidewalk warning systems installed in 2004 and 2005 observed the installations and conducted site visits twice a year for three years.
The Vermont study found that snowplows determine the fate of most detectable sidewalk warning systems in the Northeast. In some cases, edges of adhesive tiles have lifted up, becoming tripping hazards. In other cases, sections of tile had completely broken off, leaving sharp, jagged edges. In still other cases, the product material or coating had worn thin, completely broken off, or faded. All of these issues incurred high maintenance, repair, or replacement costs.
While composites are durable, they don't appear to be sturdy enough to withstand the snowplow blade. Where there are snowplows, vehicular traffic, and heavy industrial use, cast-iron and stainlesssteel products are becoming more popular. Most studies found that cast iron stands up very well.
Aluminum panels, however, did not appear to withstand snowplows due to their thickness and pliability. In colder climates, the skid-resistant coating was easily removed,exposing the underlying aluminum. Some domes were completely removed by snowplows, leaving holes for water to enter and get trapped under the panel. Stainlesssteel panels suffer the same problem. One company has improved its stainless-steel panel by adding small ridges onto the domes that allow snowplows to glide over the tops and reduce contact with the coating. Although still being reviewed for long-term durability, the small ridge panels are an improvement in areas of significant snowfall.
Water and Sealing
Several studies reported problems with stamped concrete truncated domes. Composed entirely of the top layer of the cement slurry, they do not incorporate any aggregate to give the domes strength. Therefore, this product was not accepted by many state agencies.
Today's fixtures feature precisionsegmented optics in a variety of light distribution patterns and lamp sizes and styles. Some fixtures, for example, have flat glass lenses to meet strict environmental standards; others are available with either vertical lamps for wide area lighting or horizontal lamps for roadway coverage.
Many studies also reported problems with surface-applied mats, tiles, and panels. These products fail when the installer doesn't put enough epoxy on the product or properly seal around the edges, allowing water to become trapped under the detectable warning system. This can lead to stagnation and eventually degraded subbase material. In cold climates, a freeze-heave-thaw process will cause the panel to lose adhesiveness and blow out.
The sooner the visually impaired can recognize safety markings, the sooner they can prepare for hazardous road crossings or obstacles ahead. ADAAG states that detectable warning surfaces must 'provide contrast in resilience or in sound when sensed with a cane' as well as 'offer a strong visual contrast to adjacent pedestrian surfaces.' This contrast can involve color differences or a sealer that creates a wet look.
Although durable, cast-iron panels have contrast issues. When rust from the panels bleeds onto the adjacent concrete, contrast is dulled. Also, contrast between a wet cast-iron panel and wet, aged concrete is questionable, although yearly pressure washing may be a solution. Cast-iron panels should not be used on bituminous concrete sidewalks because there is not enough contrasting color.