Engineers baffled by signalling issues on London Underground's Northern line

"Troubles on London Underground's Northern line that have disrupted journeys for millions of commuters since Sunday could persist into next week, with engineers still baffled by the cause of the signalling fault. Transport for London (TfL) is understood to be considering cancelling the weekend night tube service to allow time for extensive investigations if specialist engineers cannot fix the problem on Thursday night."

"The Northern line has become comparatively frequent and reliable since the introduction of upgraded signalling just over a decade ago. But this week's problems, with severe delays affecting all branches of the service, have been an unwelcome throwback to an earlier era when it was widely known as the misery line. Engineers have worked overnight every night since Sunday checking cables and signal boxes without identifying the problem."

"Further checks on the tunnel infrastructure can only be carried out when the line is closed. Trains normally run throughout the night on Fridays and Saturdays with the night tube, but repairing the line for commuters is likely to be the priority this weekend. The signalling system is wired, ruling out another cyber-attack on TfL like the one a year ago. Deliberate sabotage has also been dismissed due to the location of the fault."

Signalling fault at Stockwell on the Northern line has slowed services since Sunday and could persist into next week as engineers remain baffled. Transport for London is considering cancelling the weekend night tube to allow extensive investigations if specialist engineers cannot fix the issue. Trains continue to run but journeys are slower, boarding is restricted and some stations have closed due to overcrowding. Engineers have worked overnight checking cables and signal boxes without identifying the fault; a separate failure at Tooting was repaired the same day. The wired signalling system rules out a cyber-attack and deliberate sabotage has been dismissed. Further tunnel checks can only be carried out when the line is closed.

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