Design Safer Alignment at Tunnel Entrance and Exit Zone

Abstract

In order to improve the operating safety at tunnel entrance and exit zone, the alignment design of that zone was studied. By analyzing the transition character of driving environment at tunnel entrance and exit zone, the alignment transition indexes which used to evaluate the safety of alignment design of that zone 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 the difference of operating speed was selected as the medium index. Then the evaluation criteria of operating safety at the tunnel entrance and exit zone based on the difference of operating speed were put forward. Based on theoretical and statistical analysis, the relation between the alignment transition index and the difference of operating speed at that zone was modeled. At last, the recommended value of the alignment transition index for designing safer alignment of tunnel entrance and exit zone was provided.