Safety Performance of Non-Signalized Traffic Control Strategies

The Indiana safety management program targets the reduction of crashes at high-speed, two-way stop-controlled (TWSC) intersections, which are responsible for 8.2% of serious crashes statewide that cause approximately 1,000 serious injuries and over 90 fatalities annually. Key risk factors include human error, high traffic volumes, and high speeds. Despite the implementation of measures, such as alternative intersection designs and enhanced visibility, additional countermeasures are needed to further mitigate these risks at rural TWSC intersections with lower traffic volumes. Intersection Conflict Warning Systems (ICWS) presents a promising solution by alerting drivers to potential vehicle conflicts. The main objective of this study was to evaluate the effectiveness of the ICWS installed at 17 high-risk intersections in Indiana. To address the inherent selectivity bias of choosing high-risk locations, 33 additional nearby intersections without ICWS were selected as a control group. A negative binomial model was applied to identify factors that contribute to crashes and other conditions that help improve safety at these intersections. The analysis revealed that ICWS reduced the number of crashes, but its effectiveness decreased when traffic volume increased on the major road. This necessitated the development of Crash Modification Function of traffic volume on major roads instead of a single-valued Crash Modification Factor. Crash severity analysis showed that ICWS reduced the frequency of crashes at a similar rate independently of the crash severity. This finding allows applying a single Crash Modification Factor (CMF) to all the severity levels. To study the effect of ICWS on driver behavior, a portable LiDAR-based vehicle tracking system—TScan—was used. Analysis of vehicle trajectories obtained with TScan indicated no statistically significant reduction in the speed of vehicles along the main road. This result refuted the most obvious mechanism of crash severity reduction and supported the single CMF applicable to all crashes regardless of their severity. A supplemental analysis of post-encroachment times (PET) showed no statistically significant difference in short PETs between intersections with and without ICWS. In spite of the system’s obvious effectiveness in reducing the number of crashes, the findings emphasized the importance of conducting benefit-cost analyses of the ICWS safety benefits before installation, and the importance of revisiting the system safety effectiveness over time after the traffic volume increases.