You need gaps between cars, too. Two seconds of following distance in good weather conditions, four seconds of following distance in bad weather conditions.

At highway speeds, 4 seconds of following distance is 120 meters.

> You're not accounting for the space between trains.

NYC's least efficient system is block train control, requiring 300M separation between trains.

In 300M you can fit about 66 Corollas, again packed bumper to bumper. That's 66 * 5 people = 330 people, or approximately 1.5 subway cars.

Subway trains are 6 or 8 subway cars long, depending on track and time of day.

With CTBC some platforms can run at 60 trains per hour (30 local, 30 express). That's 8 subway cars every 2 minutes, or approximately 1,000 people per minute.

To move 1,000 people at all with the Corollas you will need 250 * 4.55M of them, or approximately 1.1 kilometres of cars, bumper to bumper.

>With CTBC some platforms can run at 60 trains per hour (30 local, 30 express). That's 8 subway cars every 2 minutes, or approximately 1,000 people per minute.

Unless your trains are going at 10 kph you will have more of a gap than 300 meters if you see a train every 2 minutes.

Or the trains can move much faster and much closer because of improved control.

You should recognise this argument: it's the same logic given for why self-driving will solve everything.

But you're always limited by loading time. If you take X seconds at each stop then you will end up with X * speed distance between each car. Even at 30s loading and 50 kph you're looking at 400 meters between each train.