Travel Updates


Signal Power Failure

How signal power supply failure can cause delays - and what the industry is doing to reduce them

The power supply to the signalling system can fail for a variety of reasons, for example due to a power cut or a blown fuse in the circuit.

The signalling system is designed to 'fail safe': when the power fails, the signals turn black; if the driver can’t see a green or yellow signal, they must stop the train.

What the industry is doing to reduce signal failure and resulting delays

  • Introducing uninterruptible power supplies (UPS) which take over when the main power supply is cut, minimising the delays to passengers. UPS systems were introduced on the West Coast Mainline during upgrade works and further UPS will be introduced as part of re-signalling schemes
  • For areas without UPS, ageing cable is being replaced to improve power supply reliability
  • Monitor the health of the power supply system using wireless monitoring backed up with annual inspections
  • Power suppliers notify of any planned interruptions to the power supply so backup supplies can be put in place
  • Investing in fault-finding equipment so problems can be fixed before they affect services
  • Modern “intelligent” systems identify the location of faults as soon as they occur, enabling a quick response to get trains running again
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Last updated:   16 January 2017