The DLR is semi-autonomous. It has the ability to act autonomously, but it must be started with a button and has an attendant on-board that also fulfills other duties and can be there in the case of an incident.

Indeed, it has a grade of automation of 3 (out of 4), so it is driverless, but not unattended (as that is level 4)

According to this article (https://railinsider.co.uk/2020/10/27/making-london-undergrou...), it occasionally has to even fall back to effectively level 2 operation (i.e. operator at the front of the train) because increased passenger usage makes level 3 operation as originally built (no platform edge doors or obstacle detection systems) unsafe at certain stations during peak times.

Automated trains wouldn't do that because we can design signals so that they cannot be missed (that is if you don't have positive go/no-go you stop in time)

Automated trains do have difficulties, but they are very different from the ones you see with human drivers.

The DLR (Docklands Light Railway) is autonomous, but it's a pretty slow light rail system.

I think that automation is possible because it was built de novo and doesn't interface with the rest of the rail network.