Meanwhile in more civilized places we have trains with zero staff on board, just remote monitoring (and trains which emergency stop if they lose contact with the control centre).
At some point kids chased another kid onto the tracks, was one incident.
However, as it was designed for automatic train operation from the start, it is effectively “guard (US: conductor) only operation” instead of “driver only operation”, and doesn’t have a traditional drivers cab.
Only completely unstaffed vehicles in the U.K. that I can think of are short people movers like the ones at airports. Many tube lines can be driven completely automated, the drivers job on lines like the central is basically “push go, hold deadman’s switch, push door close” and repeat, but they aren’t
In other countries on lines which are staffers vehicles there are typically far more platform based staff.
The length ranking seems to be something like:
Riyadh - 176 km
https://en.wikipedia.org/wiki/Riyadh_Metro
Dubai - 90km, first operation 2009
https://en.wikipedia.org/wiki/Dubai_Metro
London DLR - 38 km
https://en.wikipedia.org/wiki/Docklands_Light_Railway
Shanghai is probably in the running as it upgrades: