- [Narrator With only two and a half minute gaps in between trains, running a fault-free service to time will be a challenge.

To do this, they will need to use a radical new feature called auto reverse.

During rush hour, trains sometimes need to switch direction to relieve the busy central stations.

To avoid the driver having to walk 650 feet to the cab at the other end, wasting valuable minutes, these trains have a much quicker solution.

When they need to do a fast turnaround to head back into the West End from Paddington Station, the driver activates an auto reverse feature that allows the train to drive itself.

In this mode, when the computer takes over, it swaps tracks and changes direction.

As it moves back into the tunnels, the driver is free to walk to the cab at the other end of the train.

Auto reverse is key to the railway hitting its 24 train per hour target.

The early tests of its software demonstrated that it was safe.

In West London, driver Emma Knowles will be at the controls of one of the trains.

- Okay, at 24 trains per hour, this is a biggie today, but it's gonna be fine.

It's all gonna work.

- [Narrator] Emma pulls into Paddington.

- [Emma] There we go.

- [Narrator] Here, she will attempt to put the train into auto reverse to turn it around and travel back in the opposite direction.

- Is everybody off that needs to be off, 'cause I'm closing the doors now.

All right, auto reverse.

Auto reverse.

- [Narrator] With auto reverse activated, Emma's train should now automatically move forward around a mile to change tracks, stop, switch direction, and head back east into the tunnels.

- So as we come out, we're gonna come out into daylight to West Palm Park side ends, and it's safety, check there's no trespassers.

If there is a trespasser, emergency stop.

- [Narrator] For those used to driving trains manually, the auto mode takes some getting used to.

- That's scary.

No driver, that is so scary.

Mild heart attack.

(shivers) (exciting music) It's a very, very, strange feeling that I'm meant to be driving it.