Explanatory Analysis of the Safety of Short Passing Zones on Two-Lane Rural Highways

Abstract

Passing zones afford sufficient passing distance for passing vehicles on two-lane rural highways. This study aimed to assess the effects of geometric and traffic variables on the safety of short passing zones using the rate of passing maneuvers ending in the no-passing zone as a surrogate safety measure. A Poisson regression model was applied to aerial data collected by drone at seven passing zones. The findings showed that increase in the length of the passing zone corresponds to decrease in the rate of passing maneuvers ending in the no-passing zone. The passing rate is also affected by the lane width, the percentage of heavy vehicles in the subject direction, and the directional split in the subject direction. The rate of passing maneuvers ending in no-passing zones reaches a peak as the two-way traffic flow rate increases to 600 vehicles per hour regardless of the directional split, or as the absolute vertical grade increases to 4.8%–6% depending on the percentage of heavy vehicles. After the peak value, the rate decreases. The presented model can serve as a tool for evaluating and improving the safety of short passing zones.