> NYC can't even settle on a car width This is because the oldest tunnels (the numbered lines) are physically narrower than the other two systems (lettered lin

> NYC can't even settle on a car width This is because the oldest tunnels (the numbered lines) are physically narrower than the other two systems (lettered lines), so you can’t run the bigger trains through them. It would be (relatively) easy to run the narrower trains on the wider lines, but would need some retrofitting, and reduce throughput way too much.