The likely model initially is for trucks to run autonomously on highways for the long-haul part of the route, then have a human driver take over for the "last m

The likely model initially is for trucks to run autonomously on highways for the long-haul part of the route, then have a human driver take over for the "last mile" of a delivery to an urban area. The reason isn't so much security but rather that autonomous urban driving is a more difficult problem to solve. The idea of roaming gangs holding up autonomous trucks might make a good plot for a sci-fi movie, but in the real world it probably isn't as big a problem as we imagine. Most of these things are going to contain pretty mundane shipments. If you're shipping currency or gold bullion or iPhones then sure, maybe more security would be appropriate.