Sure, we have that ... right now. Called trains. Train even carry trucks. Trains are vastly more fuel efficient than trucks.
The advantage trucks have over trains is their flexibility, their any point to any other point ability. Take that out and it can be automated but that automation isn't to be more efficient than ... 19th century technology. Ha.
In my field of AI in radiology, I see a lot of people trying to completely automate things that don't have to be, and thereby fail to innovate on the particularly hard parts. Sometimes it's better to just have a human somewhere in the loop to make the harder judgement calls.
But that's not the idea. It is the camel's nose under the tent.
The goal is to get them on the road somewhere, and then gradually expand use as they can re-legislate at the cost of pedestrians.
There's a template for doing this - when cars were first commercialized, pedestrians had to be kicked off the roads, so they invented "jaywalkers", and launched a huge propaganda campaign to make it a thing[1].
Too much money and priming has been dumped into self-driving tech to abandon, so they'll try to create markets by pushing the squishy slow things that complain when they get smooshed out of the way.
[1] https://www.vox.com/2015/1/15/7551873/jaywalking-history
Take out "cars" from that phrase and I think there might be a different answer to it, sooner or later.
Specifically I liked Otto's original proposals and it sounded almost viable. The idea of having a Sacramento -> Chicago or Houston to Dallas routes for trucking with autonomous vehicles, with the last mile routes covered by normal container trucks sounded like it would work in the near term.
The fact that these are big rig trucks ensures the unit volume cost of the hardware isn't going to be a big problem (a 25k computer in a 35k car vs a 120k one in a 800k truck), the servicing can be legally mandated (patch upgrades or cleaning cameras), the power supply management can also be handled if they want to go electric with a container + rig model.
There are fewer questions about a long haul highway only self-driving route, maybe even something which will change the economics of shipping stuff through the panama canal vs going over land in a hub-spoke model without a train depot style unloading/inventory station.