Even if the tractor has to be aware of such hazards, the degree is totally different. The tractor may need to identify that something unexpected has occurred, b

Even if the tractor has to be aware of such hazards, the degree is totally different. The tractor may need to identify that something unexpected has occurred, but it doesn't need to know anything about it other than that, most likely; it can likely deal with all unexpected occurrences by stopping and waiting for someone to come manually fix it. Self-driving cars need to make complex decisions about hazards, because stopping in the middle of a public street is probably not an acceptable behavior, it may not be practical given the speeds, etc. That means the car needs to know a lot about the hazard in order to figure out what to do about it (swerve? honk? alter speed?).