Depends how either is implemented. I had to go to a town in east-central PA last weekend. Took the train. Outside of cities (per my phone’s GPS), the train was doing 110-120 mph, with not many stops. This wasn’t a “high speed train” — those were late 70s era rail cars being used between NYC and Pittsburgh.

No way a car (automated or not) being driven in a safe manner would beat that speed. Plus there’s something to be said for shared facilities, bathroom and bar car. Hard to do either in motion unless you’re in an RV.