I understand what you are saying about the highway system being subsidized, but I'm not sure I understand your reference to gasoline.
Private energy companies explore, extract, refine, and sell gasoline, with all sorts of taxes (as opposed to subisidies) along the way. What subsidies are you refering to for gasoline?
The government creates foreign policy around the maintenance of oil supplies, which has a very large cost, and is largely a gift to the oil companies. This is reflected in income taxes rather than in the cost of gasoline. There are also large tax breaks given to oil companies. Domestic fossil fuels like coal and natural gas don't get quite the same treatment, since we have plenty.
Private energy companies explore, extract, refine, and sell gasoline, with all sorts of taxes (as opposed to subisidies) along the way. What subsidies are you refering to for gasoline?