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Just as air-traffic control systems prevent planes from interfering with each other’s routes, rail signaling systems keep trains safe and on time. The Channel Tunnel Rail Link posed special challenges for signal engineers because the UK and French signaling systems are as different as day and night.
In most of Britain, signaling still consists of colored lights and semaphores positioned alongside tracks. Trains on French TGV lines, in the Channel Tunnel, and now on the CTRL use ultramodern track-to-train signaling. From transponders along the route, high-speed trains pick up digital information, which is relayed to a screen inside the cab. Drivers receive a stream of speed guidelines and other alerts, and speeding trains are automatically slowed or stopped.
Wherever the high-speed and traditional lines meet, both signal programs have to recognize each other so that they won’t compromise safety or schedules kilometers down the line. Writing the translation software required several years of planning. Designs had to be ratified by internal and external safety bodies, operators, drivers, signal committees, contractors, and Her Majesty’s Railway Inspectorate. Software and hardware were tested in a laboratory for every variable (location, speed, proximity of radio towers and generators, the strength of electromagnetic charges), then retested on-site.
“It is not solely about making your side of the railway safe, but ensuring you do not export risk onto others,” says John Benson, senior signal engineer with Bechtel in London.
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