Comments on: Platform glitch plaguing CBTC L trains

By: Paris Shows How to Automate a Subway « the transport politic

Paris Shows How to Automate a Subway « the transport politic — Tue, 30 Jun 2009 00:52:51 +0000

[...] The French city’s experience demonstrates that a conversion process doesn’t have to be intrusive. New York’s attempt at automating its L Train, a process that began in 1997, has been plagued by repeated delays, and the system still doesn’t function properly. [...]

By: anonymouse

anonymouse — Fri, 12 Jun 2009 18:39:44 +0000

Nope, the busiest lines are 2, 6, 7, and 9, all of which have 39 tph scheduled headways and 8 car trains. The circle line (5) doesn’t have quite as much service, I think it’s something like 28 tph and six car trains, and because of the peculiarities of the station layouts, the end cars are often fairly uncrowded. On the other lines, they will occasionally try to increase scheduled headways to 40 tph, but it never seems to work out, as there’s not enough room for recovery from minor disruptions.

By: A different take on the CBTC’d L trains :: Second Ave. Sagas | A New York City Subway Blog

Fri, 12 Jun 2009 15:56:36 +0000

[...] this week, amNew York’s Heather Haddon reported on some problems plaguing the CBTC tests on the L train. According to union workers who stand to lose their jobs if CBTC is deemed a success, now and then [...]

By: Alon Levy

Alon Levy — Fri, 12 Jun 2009 08:48:54 +0000

Does Moscow Metro run 35 tph with 8-car trains? My impression was that the busiest line was Koltsevaya, which runs 6-car trains.

At any rate, I think it’s just an issue of clearing the station, rather than dwells. Minimum headway equals safe stopping distance plus length of train. At subway speeds, the stopping distance is often smaller than a full train length, and rarely much larger. For instance, IRT locals seem to start braking only about a quarter or a third of the way into a station. Therefore an increase in train length translates into markedly longer headways (though total capacity still increases).

By: anonymouse

anonymouse — Fri, 12 Jun 2009 03:09:22 +0000

How does the train length affect line capacity? In terms of time for the rear of the train to clear the station, that’s only a couple seconds’ difference, though I suspect dwell time also increases on a longer train. By the way, Moscow Metro trains on the busies lines are 8-car trains of 63 foot cars, for a total of 504 feet, almost exactly the same as a 10 car IRT train, and longer than an 8-car BMT train. I suspect that the ability to run 35 tph had more to do with pneumatic doors that slammed hard and fast so nobody dared hold them (as is still the case in Moscow), more liberal signalling (fewer grade timers, more and more effective station timers), and better trained operators who knew how to take full advantage of the features of the signal system, including station timers and possibly automatic key-by.

By: anonymouse

anonymouse — Fri, 12 Jun 2009 03:04:07 +0000

There are a few components that make up minimum headway. CBTC can only improve one of them: the time between when one train starts and the following train leaves, which incidentally can also be improved by having better accelerating trains. But with a good fixed-block system with time signals or with a conventional ATC system you can get very close to the performance of CBTC, and the real limitations are elsewhere, particularly dwell time, which CBTC can do nothing about. If you want to run more trains, you need to cut dwell times, which requires much less capital expenditure and much more training of conductors and modifying train doors to close faster. By the way, I don’t think MTA can run 39 tph with its current system, nor even with its current technology, but it can and does happen with fixed block ATC.

By: Alon Levy

Alon Levy — Fri, 12 Jun 2009 00:25:56 +0000

There’s an inverse relationship between train length and the maximum number of trains per hour. NYCT used to run shorter trains, of only 6 or 8 cars rather than 10; that’s how it ran 35 tph. Moscow Metro runs 40 tph in part because its trains are shorter as well, at 6-8 BMT-sized cars.

By: Marc Shepherd

Marc Shepherd — Thu, 11 Jun 2009 14:30:38 +0000

The principle of CBTC is simply that you can run more trains on a variable block than on a fixed block. If the Moscow Metro installed CBTC, it could run more trains too.

Whether in fact the MTA could run 39tph with current technology is a dubious claim. Anonymous message board posters may say it can, but there is no evidence they’ve ever run a railroad. A few years ago, there was a quack on subtalk who made similar claims, but when he finally posted his “math,” it was full of basic errors.

By: anonymouse

anonymouse — Thu, 11 Jun 2009 05:26:28 +0000

Stopping trains at the right spot is actually not that easy for an automated system! Usually, they use a somewhat conservative approach where the train coasts the last few feet to the stopping point before applying full brake, which loses a few seconds over manual stopping and makes for a slightly less comfortable ride for passengers. My idle speculation is that NYCT has been trying a less conservative stopping algorithm in hopes of winning back a bit more capacity, but it still needs tweaking. Incidentally, I don’t think CBTC is really needed for capacity given that the East Side IRT operated 35 trains per hour in the peaks back in the 1950s, and those trains were faster too. The Moscow Metro, one of the world’s busiest rapid transit systems, has 39 tph on the busiest lines, and uses a conventional ATC system based on coded track circuits with color light signals and train stops as a backup, and all trains are driven manually. Top speed is 50 mph, (and is generally reached between most stations) and average speed is around 25 mph.

I’d recommend that NYCT install a similar system as it will provide both the speed and capacity benefits of CBTC at a much lower cost and a much lower long-term technology risk (SF Muni’s CBTC system runs on OS/2, and I think is unsupported by the vendor by now). I wonder, is NYCT planning any more CBTC installations anytime soon?

By: Marc Shepherd

Marc Shepherd — Wed, 10 Jun 2009 16:34:09 +0000

I believe the projection was that CBTC would improve capacity by 18%, not just one more train during rush hour. Lengthening the platforms is an utter non-starter. In addition to the environmental issues, it makes CBTC look cheap.