The profit incentive is much more powerful for OTR trucks.
Warehouse to warehouse, rail yard to warehouse, factory to warehouse, mostly expressway driving.
That is very straight forward, plus, loaders and unloaders are waiting for the trucks, not riding in them.
If you can couple and decouple and gas up robotically, you have a driverless truck that literally runs 24 hours a day, every day, and never gets tired, never calls in sick, and never asks for a paycheck.
And robot trucks that drive half as fast can be engineered to use one forth the fuel. Normally the extra human labor costs would offset that savings but with no human, shipping costs drop in half.