Revisiting freeway single tunnel crash characteristics analysis: A six-zone analytic approach

Abstract

Considerable studies have been conducted to investigate the tunnels' traffic safety. However, the entrance and exit parts of a tunnel are mostly considered symmetrical in previous studies, and the different lengths (long, medium, and short) of tunnels have not been separately studied. This study aims to investigate the characteristics of traffic crashes in freeway single tunnels by separately considering the entrance and exit of the tunnel as well as the different lengths of tunnels. A six-zone approach is proposed, and the data from 156 single tunnels in Hunan province, China, are applied for safety analysis. The crash rate, crash type, and contributing crash factors are compared between the conventional four-zone approach and the proposed method, and the three types of tunnels with different lengths are also compared for in-depth analysis. Results show that the proposed six-zone method provides a better understanding of the tunnels crash characteristics. The most crash-prone zones for long, medium, and short tunnels are the mid-zone, the entrance zone, and the access zone, respectively. Furthermore, at the tunnel entrance, drivers usually fail to maintain safe distance, which results in the high proportion of rear-end crashes, while at the tunnel exit, they do speeding and improper lane change that increases the risk of sideswipe, rollover, and collision with fixed objects. The study also discusses the crash occurrence mechanism for different types of tunnels. Findings of this study shed some light on the engineering and policy implications for improving traffic safety of the freeway tunnels.

Keywords: Crash characteristics; Freeway; Safety; Tunnel.