Not only that, but if a tractor encounters an obstacle in the field that it doesn't know what to do about, it can simply stop right where it is and wait for hum

Not only that, but if a tractor encounters an obstacle in the field that it doesn't know what to do about, it can simply stop right where it is and wait for human intervention, unlike cars where you don't want them stopping dead in the middle of the road. Also tractor speeds in fields are far lower than cars on roads, so automatically a huge safety advantage there.