Why don't roads and the aviation system become remotely profitable?
The Texas Department of Transportation (TxDOT) did a study on a road they built a few years back. They found that it cost a $1 billion dollars to build and maintain over 40 years. While fuel tax revenues would only be equivalent to $162 million for that amount of road for that period of time. Meaning that road only paid for about 16% of its true costs.
That's not unique to that particular road. No government owned road in Texas, or this entire country for that matter, pays for itself. Not by a long shot. Roads require direct, massive and perpetual subsidies.
Fuel taxes would have to be increased from ~$0.50 per gallon to several dollars per gallon to have any chance of paying for themselves. That's the case in Europe and Japan.
Roads are no free market. They're actually a bastion of 'socialism' and market distortions.
I don't have the data on me, but the same is true of the aviation system. Practically all airports are government financed, built, owned, and maintained (usually by state and local governments, with additional grants from federal government). And the Air Traffic Control (ATC) is run by the federal government. Aviation fuel taxes and ticket taxes aren't anywhere near covering cost of the government owned aviation infrastructure.
The ridiculous thing is that railroads are the only privately financed, built, owned, and maintained transportation system in this country. And it made a profit, up until it was undermined with over-regulation, over-taxation, and direct, subsidized competition from the government.
We used to have over 300,000 route miles of railways in this country. Today, we have less than 150,000.
Railroads still exist in this country in spite of all of this, for the same reason it was invented in the first place. Trains are the most efficient form of transport ever created. Steel wheel on steel rail has 1/10th the rolling resistance of rubber tires on asphalt or concrete. Energy requirements follow that.
No other country has engaged in such a reckless policy. In most countries, the rail infrastructure is owned by the government. Just like aviation, roads, and waterways are. And it's considered deserving of financial support just like those other modes of transportation.
Consider what China is doing with their railway system. They're adding more than 10,000 route miles. That's probably the biggest railway expansion in a century. That includes about 6,000 miles of high speed passenger rail (HSR). That's more miles of HSR, than the rest of the world combined.
Meanwhile, we just keep plucking along with the same broken policies.