Influence of Curb Return and Crosswalk Setback on Turning Driver Decision-Making and Speed Selection

Abstract

The location of curb ramps, crosswalk markings, and curb radius are important contributors to pedestrian safety at intersections, particularly for conflicts and crashes involving right turns. Drivers tend to have higher turning speeds at locations with larger curb radii, which also requires greater stopping sight distance. If the crosswalk is placed further away from the intersection corner (i.e., offset or setback from the intersection corner), it could potentially provide drivers better visibility of pedestrians and increase the available stopping distance. However, no study has previously been conducted to investigate the relationship between crosswalk location and curb radius. This paper presents the results of research that quantifies the relationship between the offset of crosswalks (setback crosswalk) and indirect safety measures (driver stopping, yielding, and speed selection) at intersections with the consideration of other characteristics during simulated driving. The study included field-based observations and driving simulator experiments. A driving simulator experiment with 50 participants was conducted to determine how setback distances, sharpness of curb radii, and presence of pedestrians affect driver stopping decision and position, and speed choice. Approximately 12 h of video (7:00 a.m.–7:00 p.m.) were collected at nine study sites that closely matched the designs tested in the driving simulator. Comparisons of drivers’ speed in a similar scenario obtained from field and simulator data were performed to benchmark the observations from the driving simulator against field data. Stop line speeds were found to be consistent between experiments and turning speeds were found to be slightly higher in the driving simulator experiment. The research results suggest that curb radius should be smaller [less than 9 m (30 ft)] to control driver speed. Additionally, a setback distance of 6 m (20 ft) is a suitable upper bound for crosswalk placement when reconstructing intersections.