If you were able to dispense with the cab and any human interfaces/amenities, that would cut out a big chunk of weight and drag. It would look radically different but just think of all of the components on a truck that are only there for the driver. No need for a cab, AC system, heater, pedals, steering wheel and linkages, airbags, seats, pretty much all of the glass and windows, doors, etc. The added sensors, telemetry, and computational requirements necessary for an autonomous vehicle suddenly don't look so pricy compared to the savings of removing a huge chunk of the vehicle, nonstop operation or maintenance, no salary for the driver, lower insurance costs, lower fuel costs, and other assorted savings. Really it's looking like more and more of an inevitability in my opinion. Once the control problem is solved, I doubt it'll be more economical to continue putting a trucker behind the wheel.

Of course if you need to provide all of that to allow for someone to drive it manually around town a lot of those benefits are gone. Who knows, there will probably be some transitional period where all automated trucks are still equipped for manual control but I doubt it'll stay that way for long.

Even if we remove all the facilities for a driver, i likely you would still need a human guard.

Although thinking about it, the guard could travel in a separate vehicle, and could be responsible for overseeing an entire convoy of trucks at one time.

I don't know what became of it, but at one point there was a DARPA initiative to do just that for military convoys. The reasoning was that automated trucks would allow soldiers to treat the convoy as a "dumb herd" that would follow and be overseen by a squad of heavily armed and armored "sheepdogs". This would improve protection for soldiers, while simultaneously improving the efficiency of battlefield logistics.

The automated part of the journey could be done by a driverless / cab-less / HID-less prime mover which drops the trailer(s) / cargo containers off at an interchanged where they are picked up by human driven vehicles for the last mile.

I don’t think so. Once you’ve already automates a truck, you have a lot more information to convey than what’s out the windshield, and you are liberated from needing to turn a steering wheel or push foot pedals.

There’s no reason to build a cab into the truck that is only used for the last mile. Telepresence will do just fine.

If that's the case, then why aren't cargo ships already automated to this extent? It seems like automating a container vessel would be even easier - there are far fewer things to run into on the water (even in a busy port) than there are on a busy highway.

I would bet because the wage paid is insignificant compared to maintenance of the vessel and that the maritime laws would be further complicating such a scenario.

Not so much maintenance as capital costs, I think. Giant cargo vessels can't be replaced as often as trucks either. But drone ships are certainly coming, it's a very trendy topic in the trade publications. I'd give it 10 years.

Pirates? You need a crew on cargo ships regardless of whether they are automated or not.

Crews generally aren't armed to begin with and with no humans to capture and ransom or threaten to change the ships course the amount of booty they could make off with is really limited. Most pirate attacks target hostages anyways. For engineering you could have small crews fly out to any one ship that's experienced engine trouble.