Well I think it could be arranged so out of the 4 trucks, only 1 could require active supervision at a time. Like 2 could be going down empty interstate, 1 is being unloaded/loaded somewhere, and 1 with active remote driver in city.

Also even if the truck needed to pull over on side of road for 20 mins until the human could take control, that would still probably be a big win compared to labor cost of 4 humans.

But yeah, trains seem like the slam dunk (but I don't know anything about the complexity of driving trains)