Effectiveness of automated speed enforcement system on expressway

Abstract

Speeding is a major risk factor for traffic safety as it increases crash occurrences and the level of injury severity. To counteract the speeding issues, the Korean government introduced automated speed enforcement system (ASES) to reduce social loss from traffic crashes. Spot ASES that enforce speeding with the measured speed at the point locations has been widely implemented in Korean roadways. As information on enforcement locations is advised to drivers via navigation and mobile application and traffic signs, drivers can avoid enforcement by momentarily diminishing their speeds at the enforcement locations. This so- called kangaroo effect may increase the risk of crashes due to sudden changes in speed near the enforcement locations. As an effective alternative, section ASES, which enforces speeding by measuring average travel speed over the section has been recently introduced. Although these two types of ASES have been deployed around the world, effec-tiveness of them is still on the subject of debate. In light of this, the present research seeks to analyze the effects of each ASES on traffic behavior and safety. To this end, Empirical Bayes (EB) Approach was used in this study to evaluate the effectiveness of traffic safety, and detailed traffic data were analyzed to unveil the behavioral changes in traffic flow. The analysis shows that drivers tend to slow near the enforcement locations. This slowing pattern, in turn, could diminish crash occurrences near the enforcement locations while the deceleration upstream indeed increase the crash occurrences. As a result, mere 7% reduction in crash occurrence was observed after the installation of spot ASES. Meanwhile, 47% reduction in crashes was observed where section ASES were installed by stabilizing traffic speed over the section. The outcomes show that both types of ASES have positive effects on traffic safety. In spot ASES, however, unstable traffic flow in the upstream segment of the spot ASES due to ka...