Head Start in Time or in Space? Determining Needed Leading Pedestrian Interval Length as a Function of Intersection Layout

Abstract

Where signalized pedestrian crossings run concurrently with vehicles, the permitted conflict between right-turning vehicles and pedestrians can be mitigated by giving pedestrians a head start. With a head start, pedestrians can establish themselves in the crosswalk before right-turning traffic can get there, reinforcing pedestrians’ priority and engendering better motorist yielding behavior. In some U.S. cities, it is becoming common to give pedestrians a head start “in time” by means of a leading pedestrian interval (LPI); however, pedestrians can also be given a head start “in space” using corner bulbouts, setback stoplines, and other protected intersection features that increase the distance from the pedestrian stopline to the vehicle stopline. A model was developed for determining the necessary LPI length as a function of an intersection’s corner geometry. Model elements include determining the path of a right-turning vehicle, defining the conflict zone, determining maximum vehicle speed, and modeling vehicle acceleration, so that vehicle and pedestrian time to reach the conflict zone can be determined. Application to a particular intersection showed that with (a) traditional corner geometry, (b) corner bulbouts added, and (c) a protected intersection layout, necessary LPI was 3.7, 1.1, and 0 s, respectively. The benefits of replacing an LPI with a head start in space included greater vehicle capacity and reduced cycle length, which in turn reduced pedestrian-, transit-, and vehicle delay and improved pedestrian compliance. To fully achieve these benefits, the Manual on Uniform Traffic Control Devices should consider eliminating its recommended minimum of 3 s for an LPI.

Prioritization of urban public transport on streets with high pedestrian volumes

“…Among the methods that increase the efficiency of unobstructed and safe passage of pedestrians through signalized pedestrian crosswalks, the authors [5,6] indicate priority intervals for the priority passage of pedestrians moving in the same phase as vehicles turning to the right. However, while time intervals can only increase the safety of pedestrian traffic by minimizing the conflict with turning vehicles, the authors [6] emphasize reducing the duration of the traffic light cycle when also using spatial priority for pedestrians in the form of a widespread sidewalk before a pedestrian crosswalk. In this case, pedestrians begin to cross the road faster, while vehicles need more time to get from the stop line to the conflict zone with pedestrians.…”