Re: Whaaat?
"The general power for systems is supplied by batteries, charged by wheel generators that only work when the vehicle is moving. "
Wellington's ones had a small motor-generator onboard for charging the batteries (old electromechanical systems means it was easier to use a small 400V motor to drive a generator and keep them charged that way.)
They also had a small onboard diesel generator (about 5kW) which was there specifically to allow the bus to be pulled to the side of the road if the power went out so it wouldn't obstruct traffic. (I only ever experienced this being used twice in the time I lived there)
Most importantly of all, they had a button beside the driver marked "emergency power cut off", which did exactly what it said. It would be "unusual" if it was absent on a Muni trolleybus or any other kind of heavy electric traction vehicle.
Without knowing the full investigation and noting the statements about thyristors, my pick is that the brakes worked but the motors weren't cut off (or possibly went to full power even before he hit the brakes), so the bus didn't stop in the distance the driver was expecting to and he didn't hit the emergency shutoff quickly enough to recover in the remaining space (or at all).
The "traction motor overspeed condition" is a good indicator it went to full power. The report states that there's an emergency power off as well as a "poles down" switch and a couple of other options.
It doesn't take much of a shunt to hurt people if they're not strapped in and anyone who's not driven a EV shouldn't underestimate their acceleration (I was surprised even in a Leaf, They get off the line and up to 30mph faster than any muscle car), so a "failure to full power" at switchon in the morning might easily result in the bus lurching forward and hitting the one parked in front of it at enough speed to hurt the driver.