That there are long stretches of road where you can't get somewhat healthy food. I have been on a road trip across Utah, Nevada, Colorado and Arizona, and outside the big citys you only get junk food at petrol stations, but no fruits, no vegetables. I guess it makes sense because salad or fresh food spoils quick and is expensive to deliver to each and every petrol station, especially if they don't have a reliable power supply in the middle of nowhere. Never thought about it before. In Germany you can get ice cream, chocolate, cake, salad or a full meal (at gas station prices, and lower quality) on the Autobahn.