I'd be interested to know how the convoy idea would deal with mundane things like slip-road roundabouts, junctions and traffic lights?
Get two or three semi trailers in a row, and then have to make sure you can get them all through said obstacle before the lights change or someone else with right of way comes along and splits up the convoy? Then all the fun and games of the leader having to slow down or stop to let the trailing drones catch up again and reform the convoy, around a busy area? What could possibly go wrong? It's hard enough to do that sometimes with a meatsack-driven convoy of cars, let alone autonomous lorries.
Not to mention the far end fun when multiple lorries arrive at once in convoy and the loading docks of the destination have to deal with them all at once?