There are several reasons why few new subway lines will be built in the US.
- Public transportation requires massive government subsidies to survive. There's resistance to pay for it, especially by people who don't even use public transportation. This is also why
you know what really requires massive government subsidies to survive? roads. because nobody pays for roads except through taxes.
In China
every high speed road is a toll road. If you don't drive you don't pay, if you drive you pay.
Every parking space is toll parking space, there is no free parking, even in your own home (you need to pay up to 40k USD for a home parking space). If you have a car you pay, if you don't have a car you don't pay.
it's all a matter of perspective. in the grand scheme of things all transportation is subsidized, whether that be through tax funded roads, or tax funded transit. it is merely a matter of which one you prefer to subsidize. they all have pros and cons.
pros of public roads + private cars: you get to build freeways through certain neighborhoods to make them into low value shitholes and keep poors in their place
cons of public roads + private cars: pollution, climate change, noise, traffic jams, high accident rates, etc.
pros of public transit + privatized toll roads: you get to move people efficiently, safely and at low cost
cons of public transit + privatized toll roads: you can't keep poors away from your ruling class with plausible deniability.