The Elizabeth line is suffering its second day of a major signalling outage which has shut down the core section of the railway.

There is no service between Abbey Wood and Paddington through the new tunnel section, and there are severe delays on the rest of the line, which runs over existing National Rail surface tracks.

The problem is due to a signalling fault on the line which was caused by overnight maintenance on Monday night, which knocked out the service on Tuesday morning and is still affecting it on Wednesday. The central core uses a newer signalling system (CBTC) compared to the older systems used on the National Rail sections (TPWS/ETCS). The outage has affected the CBTC system, supplied by Siemens Mobility, and one source has described it as “the worst signalling failure they’ve ever seen”.

The outage is having severe knock-on effects on the rest of the public transport network, as thousands of people who have migrated to using the Elizabeth line have to squeeze onto overloaded tube and rail services. The DLR between Woolwich and Canary Wharf is packed, and the Jubilee and Central lines are straining with demand.

At the moment, the focus is on fixing the problem. Every significant problem on the railway is written up afterwards and outlines what went wrong and how it was dealt with, and may be released later.

Howard Smith, Director of the Elizabeth line said: “We apologise to customers for the disruption on the Elizabeth line. We are continuing to work with Siemens, our signalling supplier, to resolve issues that resulted from overnight maintenance of the system.

“We advise customers to plan ahead, allow extra time for their journeys, and check before they travel using our website or the TfL Go app.”

Adding to the problems this morning, the Circle line has also been suspended, while the District and Hammersmith and City lines are suffering delays.

One of the key things in Thameslink core is the redundancy of the signalling system, there is the ATO (automatic train operation) in cab signalling system, if this fails there is the conventional lineside signalling system with track circuits and if this fails there are PoSA (Proceed on Sight Authority) system.  Obviously the Elizabeth Line does not have a back up system

This morning at Paddington the Circle & District platforms and the Bakerloo were closed with LFB attendance at the Circle & District Parade At entrance, I walked to Lancaster Gate saw the queue turned around and caught a train home for Paddington.

I suspect the high level of usage of the Lizzie is such that any attempt to keep carrying passengers while relying on any back-up system would lead to such extreme overcrowding with the reduced level of service it would allow that it would be worse than useless. Better to use any back-up mode/rule to get everyone safely off the trains and then concentrate on fixing the problem.  The problem affected the entire central core rather than say just a detector at one specific location which might just about have allowed a work-around.