At Dartford Tunnel, part of the Dartford River Crossing, a new PA system provides voice announcements in the confined space within the twin tunnels to give motorists messages.
At Dartford Tunnel, part of the Dartford River Crossing, a new PA system provides voice announcements in the confined space within the twin tunnels to give motorists messages about traffic situations and accidents, and also to help ensure safe evacuation in case of emergencies. It uses well over 200 loudspeakers mounted along the tunnel ceilings to achieve uniformly high sound levels of over 100 decibels in each tunnel bore. Because of headroom restrictions, size and positioning of the speakers was important – the selected low profile speakers provide the same height clearance as the existing lighting units. They also feature a very narrow sound opening designed to avoid the reverberation problems normal in enclosed areas such as tunnels. Tyco Integrated Systems of Cambridge has installed the PA, and has won another tunnel PA order for the nearby Blackwall Tunnel. The installations also meet fire and other regulations, reports Geoff King, PA sales manager for Tyco?s Specialist Communications group. As part of the project, the installer showed the feasibility of extending the existing six-zone system PA system, previously also supplied by Tyco for the nearby tunnel offices and site, into each bore of the tunnel using an existing fibre optic system, already in use for data transmission, saving cost and installation work. Once the installer had shown that the existing six-zone system could be extended to 18 zones to deliver audio throughout both tunnels, the Babtie Group Limited was appointed as main consultant and the final system designed to meet the needs of the crossing operators. Babtie Group are consultants for large infrastructure projects including transportation, buildings, public works including tunnels. The system passed all intelligibility tests for drivers both in and out of their cars, ensuring that messages and emergency announcements can be clearly heard anywhere in the tunnel. Each tunnel is divided into six individually addressable zones and messages can be delivered to any zone or group of zones.
