Examining the effects of police presence on driver behavior and collision risk at work zones

Visible police presence is an effective approach to improve compliance with posted speed limits in work zones. While police presence improves speed limit compliance and driver attentiveness, it can also contribute to sudden speed reduction and harsh braking, which may lead to traffic queues and increase the risk of end-of-queue (EOQ) collisions. Despite many studies examining the effects of police presence on driver speeds, the effects on EOQ crash risk are yet to be comprehensively examined. This paper aims to evaluate the effects of police presence on vehicle speeds, collision risk, and driver perceptions in work zones.

Speed data, collected using automatic traffic counters at six locations in a roadwork site, were analyzed using a Tobit regression model to quantify the effect on driver speeding behavior. Near-misses were identified from vehicle-trajectory analysis of video images recorded using roadside cameras and analyzed using the Extreme Value Theory approach. Driver perceptions regarding the effectiveness of police presence were gathered through a roadside survey.

The results showed that police presence was associated with a 35% reduction in the probability of speeding near where police were located and 11-20% reduction closer to the worksite. However, the risk of serious EOQ conflicts increased by around 10% when police were present. The survey results revealed mixed driver views about police presence at roadworks.

Visible police presence reduced speeding cases but increased the probability of serious EOQ conflicts.

These findings suggest that while improved driver behavior can be achieved using visible police presence, attention also needs to be given to using other safety measures to reduce the risk of EOQ crashes, when police are present on site.