I wonder how you would prevent carjackings?
The same way as it is done today. Plus the video feed from all cameras; plus an emergency signal to the trucking HQ; plus the exact GPS coordinates; plus the LoJack tag on the vehicle(s).
That is about the contents of the trailer. However if you are asking about a single vehicle, be it a car or a truck, or a tractor... they CANNOT be carjacked. You cannot threaten a robot with a gun, you cannot kick the robot out of the vehicle, and you cannot take over. Robot-driven vehicles are IMMUNE to carjacking. The most you can do is to stop them.