How a 90-second power outage sparked chaos for rail commuters

The power failure which hit a Network Rail operations centre in Manchester was a rare incident.

But after commuters were left facing chaos, it has raised questions about how a short outage at one operating centre could have a widespread impact.

Network Rail will face scrutiny for how its systems coped and responded to the outage.

That's the publicly-owned body whose job it is to operate and maintain Britain's railway infrastructure. That means the tracks, signals, embankments and major stations.

It was at Network Rail's operating centre in Manchester that the problem started. Its operating centres are where crucial controls are housed that let trains run safely across the country, with Manchester's centre responsible for large parts of the North West.

It was hit by a power cut in the area, which was resolved within 90 seconds. And despite having a backup supply, given the centre's importance, this failed to kick in as quickly as expected.

Because signalling was affected - think of that as the traffic lights of the railway - trains had to stop.

Systems had to be rebooted. But there was some damage to the systems controlling signalling, and that took time to fix because of the need to replace certain parts.

Thinking about how busy parts of the rail network are, and how many trains and crews were left out of position across the North West of England and beyond, helps explain why the impact was so big.

Network Rail has apologised to customers and opened an investigation.

Bosses say engineers have been working hard to "build additional resilience into our signalling systems to ensure that this doesn't happen again".

Network Rail has moved towards having 12 so-called Rail Operating Centres across Great Britain, replacing a previous structure of hundreds of older signal boxes. They are meant to be high tech hubs which centralise control of the network.

Experts have warned consolidating in this way means that if one centre is badly affected, the impact is much broader.

Rail writer Christian Wolmar said the problem they have created is that "if one thing goes wrong, it can wipe out, as we saw, quite a lot of the network".

"So really they've got to start thinking about both resilience, but also whether the centralisation of all the signalling and communications into a very small number of places is the right thing to do," he added.

There's nothing to specifically link this particular incident to other recent problems experienced by rail users; for example the impact of speed restrictions and infrastructure failures during the recent extreme heat.

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