And of course roads aren't used the same, just as healthcare isn't.  A guy with snow chains on his tires who drives 10,000 miles a year costs society more through his use of the road than the guy in a Prius who drives 1,000 miles a year.  The same thing with a semi-truck.  And just like a single-payer system, "there must be an amount taken from someone else to cover that difference."  The guy with snow chains is using the road more and damaging the road more, but he's not paying more.