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.