Looking at the BTS statistics:

https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pu...

you can see that 95% of railroad fatalities are classified as either "Trespassers" or "Highway–rail grade crossing". In both of those cases it seems likely that the victims are generally not actually passengers on the train, but rather are people doing something obviously dangerous near railroad tracks.

(Also the denominator wasn't clear for the quoted statistic: is it per passenger-mile, or per vehicle-mile? In any case here is a sensible denominator: https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/pu...)

It's hard to tell. 1. I can't find the 11.3 billion statistic on the Wikipedia page. 2. The stats seem to be per vehicle mile. An average train carries maybe 100 times as many people as a car. If the people on the train were driving cars there'd be 100 times more vehicle miles. 3. Are people who commit suicide by jumping in front of a train counted in the statistics? It seems that if there were no trains, some of those people would find an alternative, so it might be unfair to include them.

My point was that an at fault accident is an obvious case of a situation a human cannot handle and that it at least tells us something about the rate at which humans "disengage".

Human disengagement isn't easy to define. People don't just say "well this is too confusing, I'm just gonna turn control over to someone else". To define disengagement you need to define a performance minimum. An accident is about the lowest floor you can set to I used that. I would personally say that if you hit the brake on an on ramp while traveling slower than the highway traffic you're "disengaged." People and AI generally travel as fast as they can while maintaining a sufficient safety factor (e.g. people generally don't tailgate each other at triple digit speed and drive slower in snow). If someone's personal safety factor/comfort level requires several minutes of everyone else honking while they wait for a space fit for a semi-truck before pulling their Prius into traffic that may be acceptable to them but if an AI did that I think most people would say that's a failure even if the AI didn't turn control over to a human.