Research Completed on the Visibility of Detectable Warnings February 22, 2007

A study on the visibility of detectable warnings was recently completed that provides recommendations on color and contrast. Funded by the Federal Highway Administration at the request of the Board, the project used subject testing to determine which color qualities were most visible to people with limited vision. This information will be useful to the Board in the development of guidelines for public rights-of-way, as well others involved in specifying detectable warning products. The research report, “Visual Detection of Detectable Warning Materials by Pedestrians with Visual Impairments,” is available on the Board’s website.

Detectable warnings are used to alert people with vision impairments to hazardous drop-offs, such as those along rail station platforms, and to curb-less transitions from sidewalks to streets. ADA design requirements specify a distinctive surface patterning of flat-top domes which previous research has shown to be most detectable by cane or under foot. Existing specifications, which are under review by the Board as part of its work developing new rights-of-way guidelines, also call for a contrast in color between the detectable warning and the surrounding surface for the benefit of those with residual vision.

The new study, unlike most of the previous research on detectable warnings, focused exclusively on visual detection. With 50 test subjects, most of whom were legally blind, researchers tested and compared the effectiveness of 13 colors and patterns against several simulations of common sidewalk surfaces (white and brown concrete, gray asphalt, and red brick). Results of the study underscore the effectiveness of high contrast between warning and sidewalk surfaces. To ensure adequate visual detection, the study recommends a minimum luminance contrast (60%) and a minimum reflectance for the lighter color. The most effective warning colors, according to the results, include federal yellow (against dark adjacent surfaces), brick red (against light surfaces), and black-and-white color combinations which provided internal contrast.