CBTC on Mattapan Line

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CBTC on Mattapan Line

Postby orange1234 » Thu Jan 08, 2015 4:56 pm

I just noticed on Wikipedia that the Mattapan line is listed as operating with CBTC and the system was supplied by Argenia. Supposedly, the system was commissioned last year. Does anyone have any more details? Where did the funding come from?
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Re: CBTC on Mattapan Line

Postby BostonUrbEx » Thu Jan 08, 2015 5:27 pm

I heard it doesn't even work or does not work as intended at all. Not sure if they've ironed it out or not.
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Re: CBTC on Mattapan Line

Postby jonnhrr » Thu Jan 08, 2015 5:35 pm

I did a google serarch and found this youtube video.

https://www.youtube.com/watch?v=n9DC0Fbtfr4

Surprised we never heard about this.

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Re: CBTC on Mattapan Line

Postby MBTA3247 » Fri Jan 09, 2015 12:21 am

I believe we did hear about it, actually, just not in the above-mentioned terms. Somewhere in one of the Mattapan threads is mention of the T planning to use the Mattapan line as a test bed for some kind of collision-avoidance system prior to rolling it out to the rest of the Green Line. If this system has been put into operation, then the T did so very quietly, and it apparently doesn't work very well.
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Re: CBTC on Mattapan Line

Postby Jersey_Mike » Fri Jan 09, 2015 8:13 am

That's been in service on the line for some time. Note the video is from 2012.
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Re: CBTC on Mattapan Line

Postby F-line to Dudley via Park » Sat Jan 10, 2015 12:58 pm

Mattapan's just the designated test lab for low-key evaluation of new tech. There's nothing in-service nor any promises that you'll ever see such a system in revenue service, which is why that was not publicized. If a manufacturer's got a piece of equipment to loan for some live testing, they're just telegraphing willingness to trial it and collect whatever useful data will help them on long-term initiatives like this. I'm pretty sure the goal is to NOT commit more than a few cents in funding for tests like this and just try to milk some lend-lease usefulness out of it. Manufacturers crave opportunities to get some real-world data on their product for R&D purposes, so some free slots on Mattapan (which can spare it) for data collection presents a nice opportunity for skunkworks public-private partnerships. Nothing more, nothing less.


They've got a LOT of homework to do before CBTC can get another serious evaluation on the Green Line. The first study report got thrown in the trash because it didn't drill anywhere close to deep enough into the complexity of Green Line train spacing to draw applicable conclusions. It's very unlike CBTC on Red/Orange/Blue where there's no mystery on how to deploy the system with enhanced service density. NYC was the U.S. guinea pig for retrofitting it onto a legacy HRT system; just follow their lead and it's pretty hard to screw up. Green Line is a whole other ball of wax. Difficulty level in implementing without kneecapping headways is off the extreme end of the charts. It can be done, but it's advanced-level brain surgery and they rightfully need to study the living hill out of it multiple times over before they have enough info to attempt a deployment that gets it right. It's not for lack of courage that they don't have a plan in place. It really is that complicated to do right on a system as uniquely tight and chaotic as the legacy Green Line.
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Re: CBTC on Mattapan Line

Postby jrc520 » Sat Jan 10, 2015 8:14 pm

Couldn't we put a dummy system into place - don't do anything but let it gather lots and lots of data, and then crunch from there? That way, you can simulate to heck and back without having to ruin commutes.
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Re: CBTC on Mattapan Line

Postby Jersey_Mike » Tue Jan 13, 2015 9:52 am

The problem with CTBC is that with all the processing latencies, location error bars and safety margins, the minimum headway is longer than what is currently run with "on sight" operations.

The solution is less moving block and more collision avoidance using a combination of computer vision and radar based speed control. Basically the sort of tech being put into autonomous road vehicles. Automating an LRV is actually just a subset of automating a car because the LRV runs on rails.
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Re: CBTC on Mattapan Line

Postby F-line to Dudley via Park » Tue Jan 13, 2015 4:22 pm

Jersey_Mike wrote:The problem with CTBC is that with all the processing latencies, location error bars and safety margins, the minimum headway is longer than what is currently run with "on sight" operations.

The solution is less moving block and more collision avoidance using a combination of computer vision and radar based speed control. Basically the sort of tech being put into autonomous road vehicles. Automating an LRV is actually just a subset of automating a car because the LRV runs on rails.


No, that is not true. The HRT CBTC being installed in New York does enhance the service density. So do several other systems worldwide. Just because SEPTA bollixed it bigtime on their light rail system does not mean that is a universal condition. They have to be spot-on designed in order to maintain or enhance capacity. And that spot-on design is going to be brutally difficult to achieve on the Green Line without harming headways, and shouldn't be attempted at all until they have a spot-on design. But that is not a problem inherent with CBTC tech...it's a difficulty specific to individual lines it's being applied to. And in this case the Central Subway is way more difficult than the D, Huntington tunnel, or Lechmere Viaduct + GLX.

Red, Blue, Orange...if they templated exactly what NYC is doing we'd have better headways right off the bat (for one because Red's and Orange's ATO were far too conservative on fixed-block spacing).
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Re: CBTC on Mattapan Line

Postby Bramdeisroberts » Tue Jan 13, 2015 6:21 pm

I'd argue that trying to implement any sort of modern train control system on the GL will be utterly futile unless it goes hand in hand with major efforts to fix the central subway.

Widening tight curves, eliminating archaic non-terminal loops, and eliminating all possible switch points to simplify the Central Subway and drag it kicking and screaming out of the 19th century and allow for 21st century speeds and rolling stock in my mind is an absolute must for any CBTC scheme to work.
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Re: CBTC on Mattapan Line

Postby Arborwayfan » Tue Jan 13, 2015 6:28 pm

Which loops are the archaic non-terminal ones? (I am curious, not arguing.)
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Re: CBTC on Mattapan Line

Postby Bramdeisroberts » Tue Jan 13, 2015 6:36 pm

With the advent of the GLX and north side terminals that will generate just as much ridership as Kenmore or the B-Line, the days of Park Street and Government Center turns being necessary due to low viaduct/Lechmere ridership are gone.

Better to pair each GLX line with two western branches and allow cross-traffic to change trains anywhere between Lechmere and Kenmore as necessary. Lower-frequency C and D trains could terminate at Union, and the busier B and E trains could be paired with the busier Tufts spur.
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Re: CBTC on Mattapan Line

Postby The EGE » Wed Jan 14, 2015 9:50 am

The ability to short-turn trains to fix headway problems or to avoid issues further along in the subway will not become any less important, however. Even if most trains eventually are through-routed (and remember that the current Type 9 order only has enough cars to through-route 2 lines) there's no reason to eliminate the ability to use those loops.
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Re: CBTC on Mattapan Line

Postby Gerry6309 » Wed Jan 14, 2015 3:11 pm

Bramdeisroberts wrote:With the advent of the GLX and north side terminals that will generate just as much ridership as Kenmore or the B-Line, the days of Park Street and Government Center turns being necessary due to low viaduct/Lechmere ridership are gone.

Better to pair each GLX line with two western branches and allow cross-traffic to change trains anywhere between Lechmere and Kenmore as necessary. Lower-frequency C and D trains could terminate at Union, and the busier B and E trains could be paired with the busier Tufts spur.

As I stated in another thread, GLX will make Brattle Loop useful again since it is the only place to turn a train from the north. Brattle loop is also the tightest due to the sharp curve installed to mate it to the new NB subway in 1963. Stub end terminals such as North Station slow throughput, loops speed things up.

B should stay at Park or Govt. C should run through to Union. D should turn at North Station, E at Park St. G service (West Somerville) should turn at Brattle.
The Broadway Portal was used to turn trips from Clarendon Hill before Lechmere opened, with cars on the surface via Tremont, Berkley, Boylston and Arlington. Lechmere's purpose was to get those cars out of the Subway.

1947 Subway Routes:

9 City Point - North Station (1)
39 Arborway - Park St. (2)
43 Egleston - North Station (1)
57 Heath St. - Park St. (1)
61 Reservoir - Lechmere (3)
62 Lake St. - Lechmere (3)
69 Watertown - Park St. (2)
92 Sullivan - Bunker Hill - Brattle (1)
93 Sullivan - Main - Brattle (1)
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Re: CBTC on Mattapan Line

Postby Bramdeisroberts » Fri Jan 16, 2015 4:52 pm

My issue with the loops is that while they do awesome things for service flexibility, their age and the constraints that they place on rolling stock design have had some pretty serious repercussions for the Green Line as it's moved forward into the 21st century. The loops (and short-turn service in general) made much more sense in the age of single-car trolleys that were headed towards the central subway from dozens of different feeder lines, attracting smaller "chunks" of ridership from much more disparate feeder lines when there was no possible way to get all those trolleys through the central subway effectively. At the same time, more lenient attitudes about safety (and lets be honest, about litigation) as well as more reliable/attentive operators meant that signalling/car control placed much more emphasis on driver skill, and those skilled drivers in their peppy single-car trolleys were able push much more passenger throughput through the central subway.

Fast forward to 2015, and the GL is now this (appropriately colored!) Frankenstein's monster of a transit line that manages to combine the worst attributes of trolley and rapid transit running. You have a route map that resembles a busy rapid transit line from London, NYC, Paris, etc, with forked ends servicing extremely dense transit-dependent residential areas on either end converging on a single main line that cuts right through the densest commercial districts in the city. As a result, ridership patterns are now much closer to what you see on the IRT lines or the Central/Northern lines, and the T has managed this over the past 40+ years with the kluge solution of custom articulated trolleys designed to fit old streetcar loading gauges. Any glimpse of a B or D-line train at 8AM or 5PM will show you how well that's working.

With the litigation/risk-averse culture that we operate in, you'll never be able to push the kinds of driver-dependent frequencies that you used to in the days of trolley running, and any implementation of "improved" signaling such as CBTC will only hurt headways that much more. So you can't increase system capacity that way, and the only way to effectively do it is by increasing the capacity of the trains that you CAN run.

So the answer is clearly going to be found in your rolling stock, which leads you to the problems that the T has had finding that "magic bullet" rolling stock solution (and after 40+ years, it arguably STILL hasn't found it). The Boeings (when they ran) and the Type 7's did an admirable job of handling the 1980's ridership levels that they were designed for, but in 2015 they just can't meet today's demands in terms of station dwell times or ADA accessibility. That left the T scrambling for a low-floor solution in the LRV form factor that could fit PCC loading gauges, which got us the Type 8's and 9's, with their derailment-prone articulated unpowered center-sections. It's not that their 70% low-floor design is inherently bad, it's just that all of the systems where similar rolling stock designs work well (read: any new-development light rail in the US) have nowhere near the tight curvatures of the GL. At the same time, the all low-floor European streetcar designs (think any Citadis/Flexity tram) that could handle the GL's tight curves and loops are all much longer than the GL trains, and at the same time struggle at the high speeds demanded of GL rolling stock on the D line as well as the GLX.

This is why, if I were the T, I'd be looking seriously at what it'd cost in terms of service flexibility to lose the loops and straighten the curves so that I could combine the rollout of some headway-killing CBTC system with much larger all low-floor rolling stock (think Regio-Citadis or Flexity Link) that can handle the ridership of the B line and the speeds of the D and GLX with ease, but wouldn't fit around the loops. A pair of Regio Citadis/Flexity Link trains would get you the capacity of a Blue Line consist, but with street running and Central Subway compatibility, and it could net the T double-digit % increases in GL passenger capacity for a (relatively) small amount of money. And it would make the cost/headache of a CBTC rollout actually worth it!
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