It's still an absurd comparison. I'd venture to guess that the average combine is driven in a straight line at a set speed at least 95% of the time it's being used.
The worry for combine drivers is that last 1% of the time when they have to get that big machine (with wheels on it takes a lane and a half). Then running at 15mph they have to get from field to field. There is a big problem with other drivers (cars) seeing it from well back and not realizing it is going slow until it is too late and they rear-end it. Or they realize it is going slow in time, but because it is slow they decide to pass on a blind corner (or perhaps pass just as the combine passes a mailbox and so it cannot move over).
Yes rural roads do not have a lot of traffic, but they are not empty.
