Crash analysis of expressway long tunnels using a seven-zone analytic approach

Abstract

Research efforts have been made to understand tunnels’ traffic safety. Most of the previous studies have not considered the different features of tunnels with different ranges of length comprehensively. Generally, three- or four-zone approach has been adopted, with which the entrance and exit parts of a tunnel are considered symmetrical in the safety analysis. This study employs a seven-zone analytic approach for the safety investigation of 18 expressway tunnels with length ranging from 2 to 3 km. The results reveal that the crash rate increases firstly for the entrance zone, then decreases for the midzone and again increases at the exit zone. The high crash rates at the access, entrance, and transition zones are attributed to rear-end crashes. Although single-vehicle crashes take place in the mid and exit zones (1) at the tunnel entrance: failure to maintain safe distance; (2) in the midarea: failure to maintain safe distance, fatigue driving, overspeeding, and improper lane change; and (3) at the tunnel exit: overspeeding and improper lane change mainly contribute to the crash occurrence. Friedman test was performed to test the significance of the contributing factors. The crash occurrence mechanism is discussed for the selected long tunnels. Finally, engineering and policy countermeasures are recommended to improve traffic safety in expressway tunnels.