Well, if they're flying over the roads, it's not like they're going to look for a rest stop on their way. I don't think "Daddy, can we pull the flock over? I need to go to the bathroom" works the same way in air.
..Although... just-washed cars could be their rest stops!
I always was told that since the just washed car is shiny, to the eye of a flying bird, it appears similar to a small body of water, and most birds prefer going over water. I have no knowledge as to whether this is an old story, or if it is true.
Part of the enjoyment of being a consumer is that for every three CDs you buy, one of them that you spent $20 on is complete and utter shit. ----The Bloodhound Gang's Jimmy Pop Ali