Design Safer Alignment at Tunnel Entrance and Exit Zone

Abstract

This paper studies the alignment design of the tunnel entrance and exit zone in order to improve the operating safety. By analyzing the transition character of driving environment at the tunnel entrance and exit zone, the alignment transition indexes were established by the reasonable combination of the alignment elements, including curvature radius and grade. Due to the shortage of accident statistics, the indirect analysis method was adopted and differences of operating speed was selected as the medium index. Next, evaluation criteria of operating safety at the tunnel entrance and exit zone are put forward, based on difference in operating speed. Based on theoretical and statistical analysis, the relation between alignment transition index and the difference of operating speed at that zone was modeled. Lastly, the recommended value of the alignment transition index for designing safer alignment of tunnel entrance and exit zone was provided.