A methodology for the sizing and positioning of emergency exits in tunnels

The reference law for the construction of new tunnels belonging to the Trans-European Road Network currently calls for the implementation of emergency exits when the expected traffic in the tunnel is larger than 2000 vehicles/hour per lane and the length of the tunnel is more than 1000 m. Emergency exits must allow the road users to abandon the tunnel afoot and in safety and to reach a safe place in case of accident or fire. Apart from allowing pedestrian flow outside the tunnel, such exits also have to provide a pedestrian route for access to the tunnel by first aid services. Emergency exits can provide a path toward an emergency tunnel which leads pedestrians to the outside or to shelters with escape routes separated by the tube of the tunnel. The Italian legislative decree n. 264, published on October 5th, 2006, imposes that the distance between emergency exits must not exceed 500 m. Sizing emergency exits can be submitted to the application of the technical norms of prevention and protection by fires. The legislation related to the minimum safety requirements for tunnels of the Trans-European Road Network does not clearly state anything concerning this aspect. This paper proposes a methodology for the verification of correct spatial positioning and sizing of the width of emergency exits of road tunnels, considering such width as a function of the expected vehicular flow for the tunnel, the distance between two emergency exits, the number of lanes in the tunnel and the average coefficient of occupation of the transiting vehicles.