Impact of automatic emergency braking on the benefits of red-light safety cameras

Introduction: With the increasing prevalence of crash avoidance technologies, well-established effects of traditional safety countermeasures may change. This study examines the impact of automatic emergency braking (AEB) systems on the effects of red-light safety cameras on real-world crashes at signalized intersections. Method: Effects of AEB systems alone on rear-end crashes and rear-end injury crashes at signalized intersections were estimated using crash data from 19 states and Poisson regression models. Effects of red-light safety cameras alone on rear-end crashes, rear-end injury crashes, all crashes, and all injury crashes were evaluated by meta-analysis of 35 previous studies. Based on these two analyses, effects of red-light safety cameras on crashes were calculated assuming that 28%, 51%, 95%, and 100% of vehicles on the road were equipped with AEB systems. Results: As the percentage of vehicles equipped with AEB grows, the increases in rear-end crashes and rear-end injury crashes associated with red-light safety cameras decline, and the reductions in all crashes and all injury crashes grow. With no AEB impact, red-light safety cameras are associated with a 21% increase in rear-end crashes, a 10% increase in rear-end injury crashes, a 7% reduction in all crashes, and a 19% reduction in all injury crashes. Those figures improve in tandem as more vehicles are equipped with AEB. Assuming all vehicles have AEB, the increases in rear-end crashes and rear-end injury crashes decline to 13.5% and 5.9%, respectively, and the reductions in all crashes and all injury crashes grow to 9.7% and 20.2%, accordingly. Conclusions: The growing prevalence of AEB systems will extend the benefits of red-light safety cameras by mitigating associated increases in rear-end crashes. Estimates of the benefits of other proven safety countermeasures should also be reevaluated to account for the growing impact of crash avoidance technologies.