VEhicle headway monitoring & control for Eu directive compliance

The Roads Tunnel Safety Regulations 2007 require that traffic [in a TERN ] tunnel maintain a travel time gap of 2 seconds; or 4 seconds for a HGV. These regulations also require the Administrative Authority for the Tunnel to ensure that the procedure for that tunnel\´s immediate closure in the event of an emergency is established. Throughout Europe this is commonly achieved by installing Traffic Signals at the tunnel entry portal. Traffic congestion in a road tunnel can significantly increase the probability of occurrence of a major incident - many tunnel operators seek to avoid congestion from occurring in their tunnels. This paper describes a system which integrates a number of different existing technologies to provide a "Tunnel Occupancy Manager". It is achieved by the application of the existing principles and technology to dynamically manage tunnel traffic flows. In normal operation, the system employs ANPR cameras to monitor the speed of and headway between vehicles approaching a road tunnel. If a vehicle is identified as travelling too close its number plate could be displayed on a VMS displaying the legend "VEHICLE REG "AB57 XYZ" KEEP YOUR DISTANCE". Similarly, enforcement proceedings could be initiated. This forms a “Traffic Calming” zone on the approaches to the tunnel where traffic speed and vehicle headway are regulated. When it appears that congestion is likely to occur in the tunnel (as monitored at the exit of the tunnel in a “Congestion Monitoring zone”), the Tunnel Occupancy Manager would start to "meter" traffic through the tunnel by firstly operating advanced warning signs and then modulating the switching frequency of traffic lights located near the entrance of the tunnel via a sophisticated control algorithm. If the flow rate away from the tunnel is less than the flow r