Investigating the Speed and Rear-End Collision Relationship at Urban Signalized Intersections

Rear-end collisions are often the overrepresented type of collisions at urban signalized intersections. Although these collisions can occur for a variety of reasons, speed can always play a significant role in rear end collisions, as the stopping distance increases with speed. The study presented in this paper investigated the relationship between speed and rear-end collisions at urban signalized intersections. Collisions, speed characteristics, traffic volume, and geometry data for a group of urban signalized intersection approaches were collected for the analysis. Negative binomial safety performance functions were developed to establish the relationship between collisions and various speed characteristics, while controlling for the traffic volume and road geometry. The goodness of fit of the estimated models was checked with several measures to ensure model adequacy. The results revealed intuitive findings for various parameter estimates of the models. It was found that a 1-km/h increase in the standard deviation of speed was associated with 6.3%, 8.2%, and 5.7% increases in the frequency of total, injury, and property-damage only (PDO) rear-end collisions, respectively. For both the average and the 85th percentile speed change, the estimated collision reductions were almost the same. An increase in 85th percentile speed by 1 km/h was associated with 1.1%, 1.6%, and 0.9% increases in the frequency of total, injury, and PDO rear-end collisions, respectively. Moreover, as the level of speeding increased, collision frequencies increased exponentially. The results of the study suggest that speed management upstream of the intersection approach could reduce rear-end collisions at urban signalized intersections.