1. Channel Tunnel transport system

The Channel Tunnel transport system (figure 1 ) consists essentially of two single-track rail tunnels (north and south), 50 km in length, 37 km of which are under the sea, and a road service tunnel. The latter not only provides access to the rail tunnels (for rescue and maintenance operations), but also ensures the passage of pressurized ventilated air to the rail tunnels, enabling passengers or personnel to evacuate without the risk of smoke. The tunnels are used by four categories of international trains:

• Eurostar and Freight ;

• both categories of Eurotunnel shuttles, carrying heavy goods vehicles or passenger vehicles.