It’s not like many kids are planning to be truck drivers. It is a job that people wander into. The bigger problem will be those that are doing it when the job goes away, as well as continued pressure on the job market as a whole (what will pop up to replace the portion of the labor pool that would have driven trucks before).
I think truck drivers (especially long haulers) are safe for at least 10-20 years. But yeah, truck are probably the first road vehicles to be reliably automated.
Actually, I think that long haulers are going to be the ones that first suffer. When you need a human there anyway to sign/unload/etc, then having that human also be a driver isn't such a huge problem. With long-haul the only thing that the human really needs to do is drive, and then, if needed, you could have a staging area to get the truck into the city… in much the same way that road-trains are dealt with.
But enough to make me believe in not wanting to get a future job in driving trucks (there's a market here that pays)