Cleanliness. Find a truck stop near you, go use one of the toilets, more often than not the facilities are beyond filthy unless the station cleans them several times a day.
Gotta disagree. I've taken many interstate trips across the U.S. and must have used the bathroom in a truck/travel stop dozens upon dozens of times; I've never once seen a disaster. (No doubt due to heroic efforts by the staff, but still.) 99% of the time they have all three of soap, water, and clean surfaces. Much better luck than with auto-oriented gas stations, which often are as you describe.
