I think the term "self-driving" is preferable to "driverless" because it's not like there's no driver, the car is the driver. It's also less scary-sounding which could help speed up adoption. :)
Some jurisdictions have rules to restrict convoying, many trucks following each other as a group. I'm not sure I want to see road trains just to save a few bucks on that second/third driver.
Not having a driver in the cab supervising the robot is safer? I don't see any call to remove pilots from airplanes. And I doubt the extra 200lbs of driver makes much different given these are trucks.
Again, how does having or not having a driver in each cab affect this?
I would add that allowing multiple trucks to operate this way will require some changes to the law. And the redesign of many roads. Imagine trying to merge into traffic or onto a bridge when some vehicles are longer than merging lanes. It sounds like a great idea but isn't practical.