Some states (Iowa, at least, maybe Nebraska?) seem to have a rule that billboards have to be a certain distance away from the road - a fairly large distance. You have to work to read them. It makes them much easier to ignore.
I don't know if that's the rule for all roads, or just for interstates. I don't know if it's for driver safety if they veer off the road, or for avoiding distraction, or just to limit advertising. But I like it.
Regardless, the general feel of driving here is very different from many other states because of this rule. It's one of the first things I notice when I drive somewhere else in the US.