A fault with the signalling system between St Albans City and West Hampstead Thameslink means that some lines towards London St Pancras International are disrupted. As a result, trains running between Luton and London St Pancras International may be delayed by up to 20 minutes or revised.
Disruption is expected until 17:00.
Services running from St Albans City towards London will be subject to delays, and potential alterations.
You may need to travel on a different train to normal or change trains at an intermediate station to complete your journey.
You will be able to travel using your normal route, but you should allow up to 20 minutes extra to complete your journey.
For the latest information, you should listen to announcements, check station screens, and consult journey planners.
Planning your journey:
For help planning your journey, check live departure boards, view a live network map or see alternative route guides.
If you’re travelling within London, you can use the TfL Journey Planner.
Stay up to date on the move with Thameslink's WhatsApp channel. Live updates are available Monday to Friday, 07:00–21:00.
Can you tell me more about the incident?
A track circuit failure is disrupting trains which travel from St Albans City to London.
This part of the network uses track circuits to detect the position of trains. These are electrical systems which monitor whether a train is on a section of track. They operate as part of the signalling system, which is designed to be "fail safe".
When a track circuit fails, the signalling system will interpret this as a train remaining in place, even though there may not be a train present at all, or the previous service may have long since left the area.
As a result, further trains cannot be automatically allowed onto the relevant section of track. Train drivers will be stopped by red signals on approach. They will then get verbal permission from the signaller so that they can proceed, and will run at a heavily-reduced speed as far as the next signal. This is so that the drivers will stop safely if they see anything ahead of them.
In some areas, the sections between signals can be several miles long, so this can result in delays building up. Even with shorter sections of track affected, there would still be a delay of at least a few minutes to each journey.
Track circuit faults can be caused by a number of different issues, including electronic faults or obstructions on the track. Network Rail manage the signalling system, including track circuits, and their staff will be investigating as quickly as possible. Progress updates are being closely monitored.
You can check your journey using the National Rail real-time Journey Planner.
You may be entitled to compensation if you experience a delay in completing your journey today. Please keep your train ticket and make a note of your journey, as both will be required to support any claim.