The use of a detectable warning surface was first required in 1991 as part of the Americans with Disabilities Act Accessibility Guidelines. The surface is required for hazardous vehicle ways, transit platform edges, and curb ramps. Through changes and tweaks over time to the Americans with Disabilities Act, the warning surface is now required for any area where the terrain changes, there is a transit platform, or an intersection to a vehicle way. The purpose of the warning surface is to provide a way to detect the change in terrain for visually impaired people. To do this, the detectable warning surface has key design elements to alert the user to changes.
The truncated domes are the key element to the warning surface. There are strict regulations and guidelines to determine the spacing and height of the domes on the surface in order for the warning surface to be compliant with ADA regulations. Most manufacturers of warning surfaces meet these requirements. The truncated domes provide a different texture and feel to those moving over the surface. This change in surface is able to alert a visually impaired user that a change or hazard is approaching and to use caution. The domes themselves are hollow which helps serve a secondary purpose. When tapped with a cane for the visually impaired, the truncated cones provide a different sound back to the user to alert him/her about the changes. Also, the simple nature of having the truncated domes on the surface can provide a slip and skid resistant quality. This can be beneficial when placing the warning system on ramps.
The color of the warning surface also is a key element. There are many different colors available, and the purpose is to provide a contrast to the already existing surface. There have been studies conducted that prove that when the warning surface, even with truncated domes, is of a similar color to the existing surface, visibility decreases drastically. The difference in surfaces can be even harder to detect in low light. This makes the warning surface impractical for those that it is intended to help the most. In order to combat this, ADA regulations requires that the warning surface provides contrast. This can be done by either placing a dark surface over a light surface, or a light surface over a darker one. For this purpose, the warning systems come is a variety of colors to meet this requirement. The most common colors to see used for a detectable warning surface are black, yellow, gray, blue, or varying shades of red. It is important to note though, there is no one standard color that must be implemented in order to comply with ADA guidelines.