Assessment of the Effectiveness of the Time Based and Distance Based Surrogate Safety Measures in Mixed Traffic Environment

Abstract

Surrogate safety measures (SSMs) are an effective alternative to assess traffic safety in the absence of crash count data. Time-based and distance-based safety surrogate measures are extensively used for traffic conflict reporting. However, the threshold selection for time-based SSMs and stopping distance calculation for distance-based SSMs are mostly made based on response time assumptions. There is little research that have used calibrated response time from real world traffic to measure time-based and distance-based SSMs. This research analyzed the shortcomings of applying time and distance-based SSMs in mixed traffic environment, using real-world vehicular trajectory data. In this context, mixed traffic is defined when traditional human-driven vehicles (TVs) share the road with autonomous vehicles (AVs). We find that the surrogate safety measures’ threshold selection for mixed traffic is an unexplored area that needs to be addressed. Furthermore, our findings point to the need for the use of calibrated response time when using time-based and distance-based SSMs.