A disaster waiting to happen, imagine terrorists getting their hands on them.
Probably less likely than now given that I would have thought there will be no "cab" in the final implementation of the design. So you would have to hack them, rather than just poking the driver with a sharp bit of metal and stealing his keys.
No, all three trucks will have cabs and drivers.
On the motorway however the lead truck will 'drive' ie speed up/slow down, and the drivers in the following trucks will only steer, but that's all. When the three truck convoy leaves the motorway all the trucks will be driven independently.
The idea is that the following trucks can tailgate the one in front and sit in the slipstream and it should be safe because you have removed the human reaction time when braking or speeding up, as the following trucks will be controlled by the lead truck.
I think that one feature that should be in the final design is a huge LED TV on the back of the trucks so the drivers behind can watch porn!