Who builds and maintains the roads for your car?

Not quite the same because they don't control as easily who drives on the roads. They can easily stop you from getting on the train though.

"They" routinely close or cordon off the roads & sections. They also suspend license privilege (obviously as allowed under laws & regulations).

This would be no different than cancelling the whole train or train route; & stopping or cancelling one's entrance pass to train station.

If the government ceased to exist, the roads would still exist. I doubt the train would continue to run

The roads would continue to exist in a road usable by modern cars for only about 10-15 years. Have you been to any failed state? :-)

Good thing all those roads aren’t planned, built, and maintained by the government!

The "Libertarians are like house cats" meme comes to mind

What about a taxi? What about a private bus company? I'd argue that even if you don't like or trust your government there are environmental, economic, and infrastructure issues affecting the whole world that result from an overreliance on private cars. Surely you can find a way to maintain your liberty without having a car sitting in your driveway all day.

Hope you are digging your own fuel