They will always need drivers just to stave off banditry and handle emergencies. What is likely is a single manned truck leading small convoys of automated machines.
This is an argument I have never understood.
Do you really think the only thing preventing highway robbers is a driver? If anything, self-driving trucks would likely be able to respond more effectively as they can call police without fearing for their lives.
Without people you can also do tricks like electrifying the chassis, so anyone who tries to touch it gets an electric shock.
Or a computer vision system connected to a machine gun. (sarcasm)