Comparative study of European tunnel emergency-stop-area-wall protection measures.

Due to the increasing number of traffic accidents involving the collisions of vehicles with the emergency-stop-area head walls in tunnels, a comparative numerical analysis in accordance with the EN 1317 standard has been performed in order to assess the quality of the available protective safety barriers. Based on the simulation results, the values of the relevant injury criteria - the acceleration severity index (ASI), the theoretical head impact velocity (THIV) and the post-impact head deceleration (PHD) - were computed for several collision scenarios involving two different passenger vehicles colliding with two different safety barriers in various ways. The results show that due to the geometrical restrictions in the tunnel's emergency stop area none of the barriers can provide total protection for the occupants of the vehicle in the event of a collision. The installation of a steel-sheet-tube crash cushion was, however, found to provide the best possible protection within the given limitations. The results of the analysis were the basis for selecting a safety-barrier design for existing tunnel installations and for the proposed changes in regulations governing the geometry of the tunnel's emergency stop area.