These trucks often have 1,000,000+$ worth of cargo. That's worth a fair amount of risk and effort even if you lose 80% of it on the black market that's still better than most robberies.
Just go on an open stretch of road in the country side with a firearm and open fire through the truck windows. A truck driver isn't going to be able to defend themselves.
You might argue that this doesn't happen because criminals are afraid of getting caught by the police and sent to jail.
But, if anything, the risks would be even greater for a self driving truck that has dozens of always on cameras recording, GPS tracking, and an emergency police call system.
> These trucks often have 1,000,000+$ worth of cargo.
That's true, but the problem is which one? Most of them are dry vans that you don't know what's inside, and/or not worth the risk. My loaded trailer was once opened and they didn't touch the merchandise. The only loss was the lock.
Most Fedex trucks already have $100k+ worth of cargo and only one person driving it. Doesn't mean it's easy to rob. Going through 80,000lb of shipments to find those that are worth enough is very time consuming and the truck will be hard to hide while you're doing it.
