You're completely wrong about Federal highway spending: 90+% is funded by gas taxes and other user fee-like sources. In contrast, Amtrak is hugely subsidized on a passenger-miles basis.
Several states impose a fuel tax that's below their sales tax limit. They still need to pay for road maintenance.
"U.S. annual gasoline consumption is 140 billion gallons and growing." The federal tax is 18.4 cents per gallon that's 25.76 billion a year but you need to subtract out the oil company subsidy's, NHTSA's billion a year for safety, federal reconstruction aid after a disaster etc, and not just the new federal construction costs.
While 'free parking' is available in large sections of the country it still takes land and someone needs to maintain it. However, it's vary unusual for federal, state, or local governments to pay for such parking as part of a gas tax, it's generally taken from the budget of the agency providing that parking space.
Anyway, I responded to someone making a very specific claim about federal spending so I responded to that, state spending is a far more complex issue so here are some numbers:
http://www.taxadmin.org/fta/rate/mf.pdf
Do you really think Alaska magically get's by on 8 cents a gallon or are the diverting funds for somewhere else to pay for roads? They don't have a sales tax so the math is easy on that one.
But, now let's look at Wyoming it has a nice 4% general tax on everything and charges 14 cents a gallon for gas. Let's say gas is around 3.25 a gallon before taxes and at 4% would wait for it be 13 cents. Do you think that single extra cent is going to pay to maintain all their roads? Because if the tax was 12 cents a gallon clearly they would be subsidizing that relative to you buying say cheeseburgers and they don't exactly have a lot of toll roads. Then again, if they spent close to the same percentage on road maintenance as people did on gas then the numbers would work out just fine. But wait for it, they don't.