Intersting! I know that in the contiguous USA, you will never be more than 20 miles from a road no matter where you are, but have no idea how far one can drive from a town.
For the curious, I think that number comes from these people and is actually 21.7 miles, includes any kind of drivable surface, (like beaches and unmaintained private roads), and excludes anything that is too wet (like the middle of the great lakes or a flood plain).