“say 35% of them “
Have you seen any credible evidence that even 2% of truck stops have underage slave prostitutes? Or even underage prostitutes who do it on their own volition?
It is more likely that fewer than 35% of truck stops have any regular prostitutes. Most truck stops have pumps, convenience store and food of some kind.
Maybe all this haggling is irrelevant, until we find out how the authors of this article came up with their estimate. They may be right, may be wrong, but they haven;t given us the means to evaluate the numbers.