One of London’s oldest train depots has recently become home to its newest fleet of trains — for the Elizabeth line — and I’ve been given a look around the huge site.

At it’s simplest, a train depot is a place to store and maintain trains, but that simple description belies the huge amount of thinking that has to go into designing a train depot that works reliably.

Although the Old Oak Common site has been stabling and maintenance for trains for over a century, a brand new facility was built on the site for the modern Elizabeth line trains. A huge new maintenance shed, rows upon rows of railway to store trains, and all the office space that the humans need as well.

In here, a dedicated control room overlooks the main outdoor storage yard with CCTV monitors for the maintenance shed roads. Just one person can control the entire depot’s train movements.

The depot is split between the train drivers who work for MTR Crossrail, and are currently running services out of Paddington to Hayes & Harlington, with an aim to run all the way to Heathrow at the end of this year.

The rest is for Bombardier staff who have the maintenance contract for the Class 345 Aventra trains.

It’s also here that two large £1 million simulators are based to help train up the drivers. Unsurprisingly, using simulators can significantly speed up training as they don’t need to reserve space on the live track, and it’s a lot safer.

An instructor sits outside the main room where they can see whatever the trainee sees, and then throw problems at them to give them the experience in dealing with problems they need.

The simulators are actual Elizabeth line drivers cabs mounted into boxes that can then project the view onto panels outside to create a quite impressive representation of what the drivers will see on the line.

Right down to the distance landmarks, such as the Orbit at Stratford.

While I was there, a signal fault was created, and the driver instructed to drive under manual control until the automatic system could be brought back online.

Can you spot the problem in the screen below?

Away from the drivers, the rest of the site is given over to storing, and maintaining the trains.

A huge shed has been built by Taylor Woodrow, and they’re quite keen on its eco-credentials, from the solar panels on the roof to bore holes drilled deep into the earth for heat

The depot has 33 stabling roads, of which nine roads are inside the shed for the heavy maintenance of wheels, motors and other rail components.

One road (as the railway tracks are known) is also surrounded by a long line of huge lift-up jacks that can lift an entire Elizabeth line train up in the air for major underbelly works. Elsewhere for normal tasks, they have maintenance pits running under the trains.

One innovation is the bogie replacement end, where they are able to drop the bogie (with its wheels) into a deep pit on a frame, then it moves sideways to the storage area, while at the same time a replacement is heading back in the opposite direction. Most depots can only do one movement at a time, so doing both together speeds up this sort of work.

They also installed a wheel lathe that can reprofile worn wheels, and this one is larger than most in that it can work on all four wheels at once, rather than just two as is more usual.

Some of the roads that the trains are stored on also have two upper walkways, so that staff can overhaul the roof equipment of the trains without using ladders or cherry pickers. The overall aim of investing a bit more in the maintenance shed today is to reduce the time it takes to service a train and get it back out into passenger service.

To that end, safety has also been revamped, and they have a system of padlocks that each locks down one part of the system, such as overhead power so that staff can work on the trains. It’s designed to be impossible to reactivate anything until all the padlocks and keys are all back in their correct place, and each unit is unique so it’s impossible to accidentally switch on one train when another one was intended.

It’s going to be a nuisance if they ever lose a key.

At one side of the maintenance shed is a dedicated deep clean room. Isolated from the rest in part because the cleaning can be carried out without affecting a neighbouring train, but also for a less pleasant reason.

Sometimes trains come back to depot with human waste in them, or in the worst situation, parts of human in them, and isolating the train is necessary for decency, or crime investigations. This side of the depot also has additional washing facilities for the staff who have to undertake the unpleasant task.

Assuming a train just needs to be stored overnight and doesn’t need any work on it, then they can stay outside, where there are currently long lines of trains waiting to come into service. And at the moment, there’s also a locomotive that drags them through parts of the Elizabeth line where the electricity isn’t switched on for various reasons.

Outdoor storage can through up some unexpected problems though – with birds, and we’re not talking pooping. Not the small ones either, but crows and the like are large enough that if they fly between the overhead wires and the trains, well, it can be unpleasant. Not just for the now cindered bird, but it can also damage the roof of the train.

The problem is made worse due to the location of the depot, which is surrounded by trees, and on one side, a canal. They have a solution though, and it’s solar powered.

It’s a very loud bird scarer – that plays sounds of crows in distress, and crows fly away very quickly rather than rescue their friend. In fact, the sounds are a bit distressing to human ears as well. If the crows go away and some other large bird takes up accommodation locally, the machine can be reprogrammed to deliver the necessary sounds.

One of the other problems that has bedeviled the launch of the Elizabeth line has been getting three different control systems used on different parts of the network to handover correctly as trains pass along the line.

Here at the depot they have one section of track fitted with all three signalling systems so they can run tests on the latest versions of the control software. As the software is adapted from the laboratory conditions to the real world they keep ironing out the bugs. It could take months, or someone will spot the rare confluence of events that is causing the problems and fit it in a few weeks.

Regardless of how long it takes, trains wont be carrying passengers until everyone is convinced it all works as planned.

Down here though, a long way from the control centre is the entrance to the depot, and lurking within a shed one of the big innovations on the site.

There will be four tracks feeding trains and and out of the depot, but two pass through these anonymous looking sheds. Half the shed is given over to cleaning the outside of the trains.

But the other half contains a brand new technology – the Automatic Vehicle Inspection System (AVIS), and you can’t go inside because it uses… lasers.

Not powerful enough to cut, but its not wise to let any laser beam accidentally get into your eyes. What these lasers do is to measure the train as it passes through. Every single component that can be seen is checked with micrometer accuracy. From the pantographs to the brake pads and alignment of the wheel profiles, all are automatically checked against a base measurement and if something looks like its wearing out faster than expected, it will warn maintenance staff.

Normally, a train would be manually inspected roughly every month, but once fully commissioned, the AVIS system will automatically scan trains every two days. That will significantly improve reliability as they can pick up minuscule faults long before they start to affect the train, or the rest of the railway.

You might think a depot full of trains that aren’t needed until next year would be quiet, but it’s a hive of activity.

Drivers being trained on simulators, then taking real trains out to put practice into action, the former Heathrow Connect service that’s now TfL Rail uses trains stored here. And the maintenance work that those trains need, plus the apprentices being themselves trained to maintain them.

They’re also making upgrades to some of the earlier built trains based on learning from the construction and running process. Usually something simple like moving cables to new locations based on making maintenance easier down to changes in the main body of the trains.

We don’t know when the Elizabeth line will take trains through the core of the network, but this Western end is already up and running.

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Thanks to the Depot & Rolling Stock Asset Manager, Colin Harbord for the tour around his huge site, and TfL for arranging the visit.

Part two of the current BBC2 series on The Fifteen Billion Pound Railway is on Wednesday at 9pm.

A few more photos: