Yeah, but the demand in the 40s had a completely different pattern from today's demand, so you can't just ramp up train frequency across the system and meet it.

The L train to Bedford Ave carries way more people now than it ever did in the 1940s, when Williamsburg was a modestly dense working-class neighborhood. On the other hand, those letter lines to outer Brooklyn are much less used today than they were in the 1940s, as are parts of the system in the Bronx. And, of course, there were elevated lines over Second and Third Avenues in the 1940s.

The parts of the system that run at crush capacity are already running with the highest possible train frequency. Some of the lines might not seem maxed out on headways, but they have to deal with interlining; the frequency of the F train can't be increased because the line it shares with the E train in Queens is fully loaded, etc.

It's not rocket science. It's just called CBTC and is what the MTA has on the L train line because it was in comparison built much more recently and is "simpler". You can't stack the old cars close together until they roll out all the CBTC upgrades, which is a massive engineering project. I don't think they're as efficient as they could be, but we shouldn't underestimate the amount of work.

https://en.wikipedia.org/wiki/Communications-based_train_con...

To be fair, the 4/5 between Union Square and 125th St is a sardine can from 7-10 AM and 5-7 PM daily even when they run every 3 minutes or whatever the rush hour gap is.

That's also largely a function of poor/no subway access on the East Side. It took a long time to get the Second Ave. subway running, and that doesn't even come close to servicing Alphabet City.

The west side has multiple lines (red & blue, plus the yellow line starting around midtown) while the east side only has the green line (and the yellow line south of Union Sq.).

It's a damn shame the 3rd Ave., Subway was elevated, and they ended up tearing it down. Having the subway on one of the narrowest avenues is crazy to me, and having it be the only subway servicing the east side (which has more avenues than the west, by the way), is even crazier.

Moscow Metro does 40 of trains per hour (doesn't save from sardine can effect tho) so one per 3 minutes is not a hard limit.

The hard limit is a function of stops, layout, train length and acceleration/deceleration ability, and finally the signal system.

Each train has to approach a station, brake, stop, wait while people enter and leave, start and accelerate, all at safe distance to the trains in front and behind. Braking, standing still and starting easily add up to a minute, so a two-minute cycle time is hard even if the track layout is friendly (evenly spaced stations, no mutexes in the central area, etc).

Ninety seconds is really impressive.

40tph is rarely achieved in practice, systems which are intended for 40tph usually actually end up running somewhere in the 30-36tph range as it basically just takes one little old lady being a bit slow or one tourist bag stuck in a door to ruin the synchronisation. Still 36tph basically already feels like there are trains "all the time" and passengers learn to just "let it go" as you would with an elevator - you know another one will arrive shorty.

Getting rid of absolute block helps, a moving block system can allow the following train to enter immediately, rather than waiting until the tail of train A leaves the far end of the station before the front of train B can begin moving. But that's not exactly something you can just drop in on a Tuesday afternoon, you'd usually have to shut the whole railway, add new signal technology, re-train staff, maybe even buy new rolling stock.

Are there others that try to operate >30tph? Which ones?

I've only travelled with one 30tph (two-minute) system, it was really relaxing. As you say, it felt as if the next train was coming immediately. Quite subjectively, it felt as if the wind pushed by next train could be felt while the previous train's lights were still visible in the tunnel.

The Victoria Line in London runs 36 tph. The Jubilee Line is 30, but will be 36 by 2019. The Central Line has 35tph in the morning.

https://en.wikipedia.org/wiki/Victoria_line#Service_and_roll...

https://en.wikipedia.org/wiki/Jubilee_line#Service_frequency

https://en.wikipedia.org/wiki/Central_line_(London_Undergrou...

No subway system in the world runs 40tph with western safety standards; the Moscow Metro achieves that rate because they leave it to the passenger to clear the doors before the train departs.

St. Petersburg as well. (Actually, closer to one per 2 minutes.)