BACKGROUND: Since 2001, the Americans with Disabilities Act Accessibility Guidelines (ADAAG) have required placement of detectable warnings on curb ramps, which remove a tactile cue otherwise provided by curb faces, and at other areas where pedestrian ways blend with vehicular ways. The ADAAG defines a detectable warning as "A standardized surface feature built in or applied to walking surfaces or other elements to warn visually impaired people of hazards on a circulation path." The ADAAG further provides geometric requirements for truncated domes and stipulates a visual contrast with adjacent walking surfaces. To accommodate these requirements, different detectable warning surfaces (e.g., plastics, ceramics, brick and concrete pavers, and metal) have been developed. These systems are expected to provide long-term performance and durability by maintaining geometric characteristics, frictional properties, and other functional requirements over the expected service life. These long-term performance considerations are influenced by material properties and conditions of use, including climate (e.g., temperature ranges, sun exposure, and snowfall), maintenance practices (e.g., snow removal, use of deicing chemicals, and sweeping), type and condition of underlying surface (e.g., underlying material types, texture, and distress), construction methods (e.g., surface preparation and use of adhesives), and other factors.
The ADAAG and recent research focused on detectability; limited attention was given to (1) material requirements that influence long-term performance and durability or (2) the test procedures needed for evaluating detectable warning systems. Research is needed to (1) identify the long-term performance and durability requirements and related properties of detectable warning systems, (2) recommend test methods for evaluating detectable warnings, and (3) develop guidance on the use of these methods for selecting detectable warning systems that will provide long-term performance and durability for different conditions while meeting the requirements of the ADAAG.
OBJECTIVES: The objectives of this research are to (1) recommend test methods for evaluating performance and durability aspects of detectable warning systems and (2) provide guidance on the use of these methods for selecting detectable warning systems for different conditions. This research is concerned with material requirements and shall not deal with detectability or geometric requirements.
Status: The project is complete. The research included a review of the existing information relevant to detectable warning system designs, materials, durability, and testing; and an extensive laboratory testing program to evaluate the ability of detectable warning systems to resist deterioration mechanisms when subjected to specific exposure regimes that simulate outdoor in-service exposure. Based on this work, the research recommended set of 13 tests for evaluating detectable warning systems. The research also provided guidance on the use and interpretation of the test results of these tests to help select those systems that will provide long-term performance and durability when used under specific environmental conditions. The final report has been published as NCHRP Report 670.