I agree: automating truck driving will not decrease truck-car crashes very much since most of those are caused by the car driver.
I don't see much of a future for drone trucks, though. Instead I think the role of the truck driver will change, with less emphasis on managing the controls and more on the strategies involved. Such as selecting between alternate routes when road conditions up ahead have changed, supervising loading and unloading, monitoring the truck's performance and intervening when something-- tire pressure, fuel consumption, exhaust quality, etc-- are approaching nominal limits. The automation will function more like an airplane's autopilot, but the driver will still be needed for the executive functions.
For instance, it will be a long time before a fully automated truck will be smart enough to slow down to conserve fuel a hundred miles from a congested urban area, so that it will avoid rush hour traffic and still make delivery on time.
Drivers may be able to spend time relaxing with their feet up on the dash, but they won't become superfluous. It is more likely that their employers will assign them additional duties to fill any slack time on the roads. Like perhaps a long distance trucker able to earn bonuses for any cold-calling marketing successes he might have, or for participating in his company's astroturfing campaigns on Slashdot...