John Halsall, managing director, Southern region

Passengers will often hear talk of our signalling system, which is incredibly complex with many component parts. One of those is a track circuit, which tells the system and our signallers where trains are in what we call sections on the railway.

On Wednesday, one of these track circuits failed (the one circled and named OG in the diagram above), therefore we couldn’t safely move trains, causing disruption to thousands of passengers.

We can work around faults like these, which involve the signaller having a conversation with each train when they approach and leave the section, but this takes much longer to move trains safely through the affected section of railway. In some cases, like yesterday, it can add up to 10 minutes per train.

Despite our best efforts to get the fault resolved quickly, we couldn’t find the problem so it wasn’t possible to run a full service in the evening.

Signals need information from track circuits to safely move trains around the railway

Track circuits explained

Signals explained

Delays explained

How did we respond?

We sent a team of electrical engineers in overnight, after trains had stopped running, so they could strip the track circuit down and continue searching for the fault. To put this into perspective, a track circuit isn’t just one small electrical component, like it may sound.

This track circuit was spread over a distance of around 1,500 metres of railway, so our engineers had to strip down various electrical cabinets and then manually test for the fault, much like you sometimes see telecoms workers at the side of the road faced with hundreds of wires in a box.

What made this job even more difficult for us was the intermittent nature of the fault. The track circuit was randomly failing and then working again, so it made it much harder for us to find the root cause of the problem when it started working again.

Unfortunately, we weren’t confident the next morning that the track circuit wouldn’t fail again. So in the early hours we began an urgent review of the findings from our electrical tests to inform our next steps.

After further analysis this morning, we were happy that the circuit was safe (after 13 trains ran over successfully) and normal working resumed at 9.10am. I must emphasise that the signalling system is designed to fail-safe, which means all trains stop if there is a fault.

So what did we do during the incident?

The fault affected trains on the fast line heading London-bound between Croydon (East and West) and New Cross Gate. To get as many passengers home as possible, we continued manually talking trains past the red signal on the fast line and also sent the maximum amount of trains on the slow line, too.

As you can see from this picture below, when you move trains from the fast to the slow line, it causes congestion, as fast trains get stuck behind slower trains stopping at all stations (the trains are the black rectangles with letters and numbers – six trains in the below picture). At the heart of our decision-making for any incident of this type is how we can keep passengers moving.

We know apologies are little consolation when your journey has been delayed but we are really sorry for the problems you faced both yesterday and this morning.

I hope that this level of transparency goes someway to explaining why these issues cause so much disruption, and shows that it’s not down to a lack of care, effort or accountability.