which is why there is so much regulation on commerical (18 wheeler) freight trucking. It would make your head spin. Free market would allow you to buy your fuel in what ever state you please. But one state would get all butt hurt because insane taxes and many would simply opt not to fill up in that state. ie new york vs jersey vs Pennsylvania.
which is why the recording system is beyond complex as to fuel per mile used and recorded how many miles were driven in what state so everyone gets their "fair" share of road use/fuel tax and everyone wins. except for the truck business. but they dont matter.