And not to forget: Trucks!
The trucking corporations can save a lot of money if they wouldn't need to stop every few hours because the driver has to pause or sleep. Even if someone is still on board to drive the small streets and for loading, he would be able to rest while the truck goes down the interstate, and be fresh when he is really needed again.
Could even work for the bigger corps to have a pool of people waiting at a reststop, take over an arriving truck, drive it into the neighbourhood, unload, reload, drive back to the nearest reststop and send it on its way to the next city - and directly afterwards take over the next arriving.
Right now testing and developing the details is just way easier with smaller personal cars than big 40t machines.