Per road vehicle. But 1 train car fits what, 1.5 trucks worth of cargo? Versus 20-30 passengers. Is it better to eliminate 2 truck trips or 10+ personal car trips?

An intermodal train car with double-stacked containers will replace 4 trucks. Even a traditional box car or grain hopper is much larger volume than a standard semi trailer.

If you look at the wear and tear on the roads, then 30 passenger cars are much better than two trucks.

If you look at emissions, I guess this is a pretty close one, too. And since so much freight is already on the rail in the US, this is the much easier fruit to pick.