A Working Concept of Accessibility: Performance Measures for the Usability of Crosswalks for Pedestrians with Vision Impairments.

This research presents an analysis framework and associated performance measures for quantifying the accessibility of pedestrian crossings at modern roundabouts for pedestrians who are blind. The measures, developed undertwo ongoing national research projects, NCHRP 3-78a and NIH/NEI BRP R01 EY12894-03, attempt to isolate the components of the crossing task for a blind pedestrian into computable and replicable quantities that allow the comparison of accessibility across individuals or sites. The framework differentiates between crossing opportunities in the form of yields and crossable gaps and the utilization of these opportunities by the pedestrian. It further accounts for the amount of delay and risk involved in the crossing.The analysis framework and measures are demonstrated for two single-lane roundabouts in North Carolina, evaluated under aforementioned research projects. The application shows that the accessibility of a pedestrian crossing to a blind pedestrian is characterized by a combination of the different measures, and further depends on crossing geometry, traffic volume, driver behavior and the travel skills and risk-taking behavior of the individual. With successful demonstration at roundabout crosswalks, it is hypothesized that the analysis framework has broader application to unsignalized pedestrian crossings, including mid-block locations.