The downside is, like the Tesla owners in recent crashes, drivers letting the car do all the decision making while the driver takes a nap and rear-ends a cop.
Perfect example is our airliners that do everything from takeoff to landing yet they still crash and lives are lost. Automation doesn't necessarily make things better.
My car has adaptive cruise and I like it. The Winni View I ferried today has adaptive cruise and I like that. But is it removing me from driving and paying attention? Is it making me a better driver?
Every airline pilot is there with a boatload of professional training. Even the weekend pilot in his Cessna has professional and recurrent training. Most every car/RV driver has had no professional training other than from mom and dad or the salesman. In Arizona a person gets their driver's license at 16 and has no further involvement with DMV until their 65th birthday. Professional training? Recurrent training? Huh? My RV company made me get a CDL with an airbrake endorsement to drive all the RV's we sell. The CDL wasn't hard to get but passing all the tests did require serious study. My CDL must also be renewed every 5 years. Should the everyday driver have the same same standard as a CDL? It's a start.
I think that before we automate cars, trucks, and RV's we first train the drivers to a higher standard. Professional training with re-current training just like in aviation. If people had to go through what a pilot has to endure 1) we wouldn't have so many drivers (gridlock would also go away) and 2) the drivers we do have will be a more mature and capable driver. It won't make the roads perfect but it will make them substantially safer. Then, perhaps, we might consider some automation.