Eurostar. Buy tickets online, walk up to gate, QR code beeps on a little scanner, walk onto train. That was it. No TSA-like security experience, no person checking anything (except one guy who walked around on the train and scanned one ticket which registered all our tickets at once, pretty uneventful). UK is a notable exception but they’re also kind of insane about government surveillance/security, especially post-brexit. Also not EU.
I don’t think it’s unreasonable to require you to buy tickets ahead of time when you’re going to other countries. All travel requires this and taking autonomous cars across countries is generally not a realistic option nor will it be except in edge cases (and for deep pockets).
Anyway point is daily train travel is generally easy and affordable. It’s not this grueling, burdensome process in places that have actually invested in it. It can be a great way to move lots of people consistently, and a lot of the US would benefit from it. Sooo many cities with crazy traffic between them forcing what should be a 30-60min trip into hours. A train would rip between these places.
Daily commuter trains between Austin/dallas/Houston for instance would be great. Austin to Dallas is a 3-4hr drive. A TGV, decades old tech, would do it in 60min flat. Could you imagine?