There's not really a way to have this discussion without being ideological but military contracts, fossil fuel production subsidies (yes there is a tax on the fuel, but also a subsidy to the people pumping and refining it), and municipally-financed airports (including the tax subsidy on muni bonds) all seem to be pretty direct subsidies that the air travel industry would not exist without. Air traffic control is also a 100% governmental function that is necessary for the industry to exist.

On what you would probably term the more ideological side, there is noise pollution, environmental costs (this one is admittedly likely a wash -- it's not as if our airports would be nature reserves if they weren't used for aviation), and presumably a major hit to revenue and quality in major metro areas -- is O'Hare really the best possible use of that extremely extremely valuable piece of Chicago real estate, or could it generate more revenue for the city and happiness for citizens as housing, shops, commercial and industrial space, and parks?

Anyway have a good day. I'm glad you're a fan of motoring and aviation and hope it brings you great joy.

I don't get much joy from long distance travel in any form tbh ;) I keep posting in this thread because people keep making untrue claims about transport economics, and it's important to be realistic here.

So we go unto the breach once more: in the USA the government run parts of the air system are funded by taxes on fliers, not direct subsidies. ATS is a part of the FAA which is funded by such taxes:

https://usafacts.org/articles/who-funds-the-faa-you-whenever...

Airports usually fund themselves via fees charged to airlines, which are then ultimately charged to the flier. You can see them in the fare breakdowns sometimes. I'm sure there are tiny airports in the US that are subsidized because governments love subsidizing uneconomic things for prestige reasons, but it isn't structurally needed.

In the US, fuel taxes and tolls combined only cover about 35% of the cost of building and maintaining roads. The rest of the cost is covered by the federal, state and local governments.

That's because gas taxes are an unusually live wire in US politics, not because roads are fundamentally uneconomic. Until 2008 gas taxes did cover highway spending, and they now require general transfers because gas taxes weren't indexed to inflation. According to this website the taxes weren't increased since 1993, so in practice the US system has been deliberately starved of sustainable revenue.

https://taxpolicycenter.org/briefing-book/what-highway-trust...

"Congress could pay for projected highway and mass transit spending by simply raising the federal tax rate on gasoline and diesel fuel. Increasing those rates by 15 cents per gallon along with indexing the rates for inflation would increase federal revenues by $240 billion over ten years (CBO 2022)."

Balancing the highway books in the USA would be easy, and it's done already in most other parts of the world.

You've now admitted that most of the cost of maintaining and building roads in the US is borne by government subsidies.

I just looked up how Germany funds its road network. It turns out that 2/3rds of the funding comes from taxes (subsidies, in other words).[0]

0. https://bmdv.bund.de/DE/Themen/Mobilitaet/Infrastrukturplanu...

Funding is a subsidy only if it comes from tax/borrowing sources that aren't related to the thing being subsidized. If taxes levied on driving fund driving, that's not a subsidy. Also that page seems to be talking about all transport including railways, but we're only interested in roads here.

Germany spends ~16B EUR per year on roads at the federal level:

https://www.statista.com/statistics/1293915/federal-expendit...

The amount it gets from motor taxes is vastly in excess of that:

https://www.destatis.de/EN/Themes/Society-Environment/Enviro...

That's not surprising because Germany has the highest motor taxes in Europe:

https://www.acea.auto/press-release/motor-vehicle-taxation-b...

The US does subsidize roads but it doesn't have to, hasn't done so in the recent past and arguably shouldn't be doing so.

Germany is highly federal. The federal government only covers a portion of the cost of road construction and maintenance, with state and local governments carrying much (a majority, I think) of costs.

From what I see in your 2nd link, motor taxes do not even cover the federal government's contribution to road construction and maintenance, not to even mention what state and local governments pay.

You're saying the US doesn't have to subsidize roads, but removing that subsidy would require the US to raise fuel taxes and tolls by 200%. Rail can also break even if prices are increased. The reason governments subsidize HSR is because it has positive externalities.