It seems like it might be actually. A dedicated smart-lane without ped access, running road-trains of trucks seems a lot easier to maintain than a rail network.
I'm also willing to bet that trains are much easier to maintain in aggregate then the same amount of capacity in trucks, due to there being fewer individual engines/motors needed. Track maintenance is slightly harder than road maintenance, but probably not harder than roads plus whatever solution you'd need for an automated truck to make it across the country (charging stations, electrified roads, etc.).
If you operate dedicated routes that have limited interaction with traffic you found achieve higher efficienct, but now people are being dropped off at what is functionally a bus stop and have to walk to work. This could actually work really well, except choke points like highway ramps will wreak havoc.
Building an entire extra set of lanes everywhere is prohibitively expensive, and even then is only feasible in the outlying areas
It's a very challenging problem in terms of space utilization and management, even if the technology magically worked in the best possible way. AV only solves some of it