I was just wondering what the average share of the highway budget most Americans would pay if it were divided according to the "benefits received" principle (i.e. how much you use it). Turns out, on average, if you mostly commute on federal roads (not a horrible assumption, but we could easily just assume that the per-mile cost is the same for federal roads as state and municipal roads and be OK) then it would be about $110, just for your daily commute to work.
According to the Department of Transportation there was about 43.5 billion allocated to federally-maintained highways in 2008. The total vehicle-miles traveled was about 3.03 trillion for the same year. The average commute (according to an ABCNews survey) is about 16 miles each way. So if you work 5 days a week about 48 weeks out of the year, and have an average commute, you'll travel about 7680 miles per year just to get to and from work, or 0.0000002535% of the total highway vehicle miles traveled. So if you paid that "share" of the transportation budget, that would come to about $110 per worker.
So you might say, "GREAT, PRIVATIZE THE ROADS OVER TO THE MARKET!" Not so fast! If we ran things according to the market, many of you suburban republicans would have a higher than average commute, especially you folks in big urban-sprawl areas like St. Louis or Dallas or Chicago. Plus, some people may not use roadways at all, or they may "use" them much more lightly. I travel 3 miles and ride a bike. Why the hell should my tax dollars subsidize some jerk with a full-size pickem up truck that does more road damage??? Some folks would call that downright un-Amuhrrican! Clearly some folks should pay more. Plus, whoever owned the roads would have a monopoly, so they'd be able to price-discriminate and charge double from 7-9am and 4:30-6:30pm, and make a tidy economic profit off the deal. So you'd probably pay at least 2 or 3 hundred a year to the private company. So, on average by privatizing certain things (or not having regulation) we probably end up saving 100 so that we can pay twice or thrice that, i.e. bending over a dollar to pick up a dime.