Where does the saving come from if they still require a driver? From the article, it sounds like the biggest gain is probably in hiring. Possibly also additional savings in fewer accidents. (lower overall fatigue)
Say currently one driver can drive 8 hours per day. So if you need to drive for 24 hours, it's going to take 3 days. If you had 3 lorries doing that journey, it would take 3 days.
But say you had your semi-autonomous road train. Now you could do the journey in 24 hours. One driver drives for 8 hours, then the next guy, then the next guy. The two lorries behind just tag along.
Imagine 3 x 25 hour journeys, where the destinations didn't quite match. Previously this would take 4 days. This time: there's 24 hours of shared journey and an extra unshared hour of travel at the end of the route. Now your drivers have to split up at that point. The guy who was driving the road train last will have to wait 16 hours, so his journey takes 24+17 = 41 hours; the guy who was driving before him will have to wait 8 hours, so his journey takes 24+9 = 33 hours; the other guy can jump in his lorry and go straight away, so his journey takes 25 hours.
Actually, why aren't there fully autonomous freight trains on railways yet? We have driverless commuter trains (Docklands Light Railway) why not the same for long distance freight? The infrastructure is there - automated signalling devices in cab, it doesn't seem too big a leap. One hurdle might be unions, I recall ASLEF or someone got upset about the DLR when it first appeared?
in Australia there are a few automation projects for mining rail.
Perhaps trains would form spontaneously as automated trucks encountered each other? You can't plan it too tightly because one might be late. So it sounds like every truck will still need a driver ready to be the leader or on their own.
Keep in mind that one reason trucks are so much more popular than rail trains is their flexibility. One by one as they're ready and different start and end points each.