I don't think that's the right metric, tbh. Even if you swapped out every paved road with a train track, they would not have anywhere near the same utility as trains. Trains have much higher capacity and efficiency but much lower granularity than cars, they fit into a different part of the problem domain of logistics. And while yes, using cars as a one size fits all solution sucks, the same is true for trains -- hell, at least while inefficient AF, cars do actually function in this environment, while trains are flat out incapable of addressing our modern day logistical needs.

Also, fairly sure dirt roads are hella cheap.

My point isn't that we shouldn't reduce cars, it's that reduce and eliminate are different things. And as long as cars exist, it's hella stupid to object any improvement in them. (The self-driving thing is in fact stupid though, but that's because it's proven to be a ridiculously hard problem that we do not yet have adequate solutions for, not because it's not something that would be helpful if we managed to crack it.)