PEL Services deploys public address safety system at M25 Dartford Crossing, UK

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A vital new traffic safety system has been installed on the UK’s busiest estuary crossing using Bosch’s sophisticated public address equipment, without it causing unnecessary noise pollution.

The new traffic safety system at the Dartford Crossing on the M25 London Orbital Motorway is designed to: automatically detect and identify vehicles that may pose a safety risk because they are oversized or carrying dangerous loads; safely escort them through the tunnel or redirect them to a suitable route; alert drivers in the event of an incident and stop all vehicles entering the tunnel.

Noisy road and traffic conditions meant that a high-quality public address (PA) system was required to communicate with drivers. PEL Services designed, supplied and commissioned a sophisticated Bosch PA system, incorporating ambient noise sensing to automatically adjust sound levels to compensate for substantial variations in the levels of background traffic noise. The system has been set by PEL to maintain the sound level at 5dB above ambient levels, in real time, to ensure announcements are audible, but not anti-socially loud.

Peter Mapp, the acoustic consultant on the project, made dB and noise spectrum checks, around the clock, in various traffic and weather conditions, in order to establish the dynamic range that would be faced by the system. He also devised the PA system concept and speaker layout. PEL Services designed the system with a Bosch Praesideo digital PA system at the heart of it, with master and slave network-controllers.

Unlike traditional PA systems, Praesideo uses a network configuration rather than having all system elements connected to a central controller. By connecting the network ends together, a ‘redundant’ loop is created, so that any break in the cable does not affect operation; an important consideration in this type of safety.

PEL has installed 12 Bosch LBC 3432-03 uni-directional projection speakers to work with the Praesideo amplification at four locations; three speakers on each pole, at different heights to cater for the varying vehicle dimensions. The speakers have been configured by PEL in a contingent redundant arrangement, as an additional failsafe. There are three amplifiers for each location, including one on standby, and the entire system is connected to an uninterrupted power supply. As a final added precaution, PEL conducted a full FAT (Factory Acceptance Test) trial at its premises before delivering the system to site.

PEL’s technical director, Vic Swain, said, “In this project, it is the designed intelligibility of the vital PA output, delivered in harsh windy conditions, directly to drivers of various vehicle-types, which makes the system work for drivers, while reducing congestion for passengers on the surrounding road network. We are proud to be part of a project where quality, control and resilience are key attributes.

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Tom has edited Traffic Technology International magazine and the Traffic Technology Today website since he joined the company in May 2014. Prior to this he worked on some of the UK's leading consumer magazine titles including Men's Health and Glamour, beginning his career in journalism in 1997 after graduating with a law degree from the London School of Economics (LSE).

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