Evaluation of postencroachment time as surrogate for opposing left-turn crashes

Highway safety evaluation has traditionally been performed by using crash data, although this method has limitations in terms of timeliness and efficiency. Previous studies show that the use of surrogate safety data allows for faster evaluation of safety in comparison with the significantly longer time horizon required for collecting crash data. However, the predictive capability of surrogate measures is still an area of ongoing research. Previous studies have often resulted in inconsistent findings for the relationship between surrogates and crashes, one of the primary reasons being inconsistent definitions of a conflict. This study evaluated the effectiveness of postencroachment time (PET) as a surrogate measure for the propensity of crashes between left-turning vehicles and opposing through vehicles at four-leg signalized intersections. The primary method of data collection was through video recording with post-processing. Custom semiautomatic video processing software was used to reduce the video to a usable format for analysis. The study evaluated the effectiveness of PET as a surrogate measure by comparing three variations of the PET measure with crash history. This comparison showed that the threshold value of PET played an important role in establishing its correlation with crashes, with the best results at a threshold as low as 1 s.