[majewsky]

I believe the main reason is the long tail of unexpected events. For instance: I regularly use the tram. Every few months or so, the driver has to get out to manually operate a railroad switch that does not react to the wireless control signal. If you had a driverless tram, the tram would have to wait for personnel to arrive at the switch for the manual override. Extrapolating from my experience manual overrides are probably necessary a few times a day across the entire city's tram network, so we'd be looking at massive interruptions multiple times a day that cause cascading delays throughout the whole system.

So unless you put in a lot of engineering effort to get rid of these unlikely-but-still-common problems, running a driverless operation is going to be more disruptive and less cost-efficient than paying the driver salaries.

[iso1631]

It's also a cautionary tale for self-driving car advocates. Running a driverless train on segregated track with signalling is far easier than running a driverless car on a mixed street with lidar.

Yet it still has enough edge cases to mean it's not worthwhile