Air traffic systems aren't a good analogy - for the most part, they're funded through user fees. Eighty percent of the FAA budget [1] is funded through the Airport and Airway Trust Fund, which is based on taxes and service fees levied on operators and passengers. This was designed to allow the agency to grow with the size of the industry, without taking over the federal budget. It's also more progressive, since air travelers are generally wealthier, it makes it so you don't have to subsidize travel for the rich with taxes on the poor and middle class.

Airport construction follows a similar system. Most airports in the United States are public-private partnerships. They issue Airport Revenue Bonds, which are similar to municipal bonds from a tax perspective, but they're backed by airport revenues, not municipal tax revenue.[2] The airport authority has to pay back the debt through the fees they collect from operators or concessions. The latter is why everything from bottled water to rental cars is more expensive in an airport. It's not just that they have a captive audience, it's that concession sales actually pay for the operation and expansion of the facility.

In both cases - the FAA and capital expenditures - it's mostly paid for by the users, not the taxpayer.

[1] - https://www.faa.gov/about/office_org/headquarters_offices/ap... [2] - http://www.nap.edu/openbook.php?record_id=14041&page=12