Sight Distance for Disabled Pedestrians at Crossings

Abstract

When crossing at and near intersections and bends with restricted visibility, pedestrians, particularly disabled people, need to estimate safe gaps in vehicular traffic, as is typically required when they cross straight highway segments. Restricted-visibility crossings occur in urban areas and in rural places such as trail crossings where horizontal or vertical alignments or both reduce sight distances. Pedestrian crossing times currently in practice in the United Kingdom and United States are based on crossing speed and crossing distance. But pedestrians also require an initial observation–reaction time, consideration of the crossing unit's length (up to 2 m), and a safety margin, all totaling 30% or more in greater total crossing time. These elements are identified relative to sight distances, on the assumption of a pedestrian's perceptions of what determines his or her safety rather than vehicle stopping distance. The conceptual elements of a crossing pedestrian are then examined to draw selected methodological parallels in collision avoidance analysis. Specifically, human factors involved in drivers’ crossing of major roads and negotiating of railroad crossings provide common features of comparable human factors and physical trajectories. Similarities with and differences from a disabled person crossing a road are then highlighted and illustrated in time–space diagrams. The conclusions are that pedestrian observation–reaction time, the crossing unit's length, and the safety margin—all currently not considered—may benefit from further examination to determine actual crossing times for design purposes accurately and thereby to improve the mobility of disabled people and pedestrians in general. Current guidance is compared with the findings and leads to suggestions for further research and application to facilities design.