>Then it should close at night.

No, it shouldn't, and I take it by this statement you don't live in NYC. I do, and have lived in Tokyo and other cities with excellent mass transit. While Tokyo's system is much, much better, it's pretty fantastic that I know I can always get a train home no matter what time it is, no matter where in the city I am, much faster than any ground vehicle would take me.

Everywhere else just runs replacement buses at night and it's fine. Yeah ok it's a little slower, but it means you're not running a huge train for five people.

There are way more than five people per train at any time of the day or night. Besides all the people with night and early-morning jobs, there's also the fact that bars are open until 4 AM. They call New York "The City That Never Sleeps" for a reason.

Many larger cities in Europe run the metro continually from Friday until Sunday night.

This is a decent compromise.

Even though trains are scheduled through the night, they shut lines down pretty frequently during overnight and weekend hours and replace them with bus service.

Part of what makes the subway system worth bragging about is that it runs at night.

I am proud of that as a New Yorker, but I would much rather replace it with buses at night if that would make it actually work during the day.

Why? Surface buses can run quickly at night when there is light traffic, and the air quality is far better at surface level than in the subway.

What city in the US has a subway system worth bragging about? Philly's subway has 3% of the ridership of NYC's. It's not even in the same ballpark.