In an emergency, special radio break-in messages on RDS car radio can provide information or instructions, and the Public Address system makes sure that people hear messages even during an evacuation. CCTV cameras will also allow tunnel operators to monitor traffic throughout the tunnels. The entire system is controlled via a single SCADA integrated control system provided by Tyco Control Systems which links all the facilities together - it can even deliver pre-recorded messages automatically when sensors detect incidents or traffic problems in the tunnels.
"This system is one of the first fully integrated systems of its kind and involved all three of our core groups covering Traffic and Transport, Wireless Solutions and Specialist Communications such as PA," said Phil Ford, MD of Tyco Integrated Systems. The automatic CCTV incident detection system can detect slow or stopped traffic, pedestrians and other traffic hazards in the tunnels, whilst the digital Public Address system allows voice messages to be broadcast to drivers manually, or triggered automatically as a result of incidents (e.g. from the motion detection system) via six separate zones of loudspeakers. In addition, a cellular mobile phone enhancement system provides full mobile phone coverage in the tunnels in emergencies, and a public radio re-broadcast facility allows uninterrupted listening to car radio programmes and RDS traffic news while driving through the tunnel.
The PA set-up is based around Philips Praesideo digital public address system covering six separately addressable zones via specially designed loudspeakers in the tunnel and the entry/exit areas. A microphone desk in the control room allows manual messages to be broadcast to any zone, and systems inputs from the SCADA system allow programmable pre-recorded messages to be automatically broadcast to selected zones in response to events or alarms. The high power audio amplifiers are equipped with fault monitoring, and all audio channels have their own audio processing and equalization facilities.
The entire system is controlled via a network controller, which not only monitors and reports on all 61 devices, but also stores seven different attention and 45 alarm tones, and up to 256 pre-recorded messages. Up to four different messages can be broadcast to different zones at the same time. These are stored as digital WAV files and the system uses fibre-optic cabling for high reliability and sound quality.
When it was first opened in 1897, Blackwall Tunnel was the longest underwater road tunnel in the world. It was originally a single bore tunnel, and a second bore was added in 1967 to cope with growing traffic. Today it continues to be a key link in London’s traffic system and carries some 100,000 vehicles a day.
(Ruth Rossington)
