Comparing safety performance measures obtained from video capture data

A comparison of safety performance is carried out using measures obtained experimentally from a video-taping of traffic operations at an urban roundabout situated in Cosenza, Italy. Safety performance is expressed from the perspective of “rear-end” vehicle interactions using five different expressions: Maximum Deceleration Rate to Avoid a Crash (DRAC), Time to Collision (TTC), Proportion of Stopping Distance (PSD), Time Integrated Time-to-Collision (TIT), and Crash Potential Index (CPI). Differences in safety performance are discussed with respect to the type of measure, traffic conditions and differences in roundabout geometric attributes. The results of this analysis suggest that safety performance is highly sensitive to the way it is measured, such that, different measures can highlight different locations or geometric features of the roundabout as posing potential safety problems. This study underscores the usefulness of safety performance measures for providing meaningful experimental indicators of potential safety problems at roundabouts, and how these problems can be affected by changing traffic conditions.

A comparison of safety performance is carried out using measures obtained experimentally from a video-taping of traffic operations at an urban roundabout situated in Cosenza Italy. Safety performance is expressed from the perspective of “rear-end” vehicle interactions using five distinctive expressions: Maximum Deceleration Rate to Avoid a Crash (DRAC), Time to Collision (TTC), Proportion of Stopping Distance (PSD), Time Integrated Time-to-Collision (TIT), and Crash Potential Index (CPI). Differences in safety performance are discussed with respect to the type of measure, traffic conditions and differences in roundabout geometric attributes. The results of this analysis suggest that safety performance is highly sensitive to the way it is measured, such that, different measures can highlight different locations or geometric features of the roundabout as posing potential safety problems. This study underscores the usefulness of safety performance measures for providing meaningful experimental indicators of potential safety problems at roundabouts, and how these problems can be affected by changing traffic conditions.