Public meeting on Green Line issues on 1/17/13

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Re: Public meeting on Green Line issues on 1/17/13

Postby boblothrope » Wed Jan 23, 2013 1:35 am

CRail wrote:Many of the delays, slow downs, and hold ups on the red and orange lines are caused by automatic operation.


No, they're caused by poorly designed block lengths and locations, and bunching at chokepoints (slow crossovers at terminals, and the crowded downtown stations). Those problems are independent of whether the controls are driven by a human or a computer.

Sometimes bunching is also caused by drivers who go slow, or take slightly longer to get the doors open, closed, and get moving again. It only takes a few extra seconds per station to add up to a few minutes lost on a run, which causes bunching with the following train, which will then get delayed at the terminal.

CRail wrote:The signals at junctions, however, are set up to detect the first train which arrives at the junction and set its route before giving a good indication. A train must first arrive, establish priority, and have its AVI read before the signal can clear up.


They should leave the busier route green by default. And/or have the detection occur further back in the tunnel, while the train is moving. If detection fails for some reason, then the light would stay red.

Busy roads don't have 4-way stops at every intersection. Neither do the heavy rail lines. There's no reason why Green Line passengers should have to endure them.
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Re: Public meeting on Green Line issues on 1/17/13

Postby Disney Guy » Wed Jan 23, 2013 10:53 am

On the green line, are there some signals that are normally red (not the double red at switches) that have a timer that begins counting down long before the train gets there? If the train decelerates at the proper rate then the signal would clear before the train got to it and had to stop. The incline inbound from Science Park is a good place for such timed signals.

Once (in the PCC era) I was on a train going at a good clip from Boylston to Arlington when all the trolley poles went off at the same spot in sequence. Shortly thereafter one of the signals in that area was set to stay as red until a train approached and it stayed that way for months. To think they could have repaired the overhead wire more quickly.
(To the theater stage manager) Quit twiddling the knob and flickering the lights while the audience is entering and being seated. (To the subway motorman) Quit twiddling the knob and dinging the doors while passengers are getting off and others are waiting to board.
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Re: Public meeting on Green Line issues on 1/17/13

Postby CRail » Wed Jan 23, 2013 12:47 pm

boblothrope wrote:No, they're caused by poorly designed block lengths and locations, and bunching at chokepoints (slow crossovers at terminals, and the crowded downtown stations)...

I didn't realize you had some source of knowledge more vast than those who run the system [whom are my source], please cite it!

Choke points: Havard Curve, where the train is limited to 10mph until well clear of the curve, and then several times afterwards when the code continues to fluctuate. That's an automatic operation slow down which manual operation wouldn't have.

Junctions: Approaching Ashmont, if a train is lined into the southbound lead, it receives a proper code into the station. If it is lined to cross over to the northbound lead and change ends (which is more common), it receives a 25 (approx) code from a short way south of Shawmut Ave. all the way into Ashmont. This wouldn't occur with Manual operation.

Stop codes: Trains relatively frequently hold stop codes preventing their movement for various reasons requiring manual override to get them into a station. Each of these instances require dispatcher attention to get permission for such, increasing the delay and potentially holding up another issue waiting for a dispatcher's response.

So thanks, by detesting my argument's validity you simply helped to support it.

boblothrope wrote:They should leave the busier route green by default... Busy roads don't have 4-way stops at every intersection. Neither do the heavy rail lines. There's no reason why Green Line passengers should have to endure them.

No, they shouldn't. You can't have a permissive signal drop, and you can't change a route once it has been established. That's rail safety 101. Heavy rail lines are centrally controlled, the green line is not. Busy intersections are not underground, they aren't on rails, and they sometimes require a stop and wait even when there is no conflicting traffic. The current set up at junctions is appropriate.
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Re: Public meeting on Green Line issues on 1/17/13

Postby boblothrope » Wed Jan 23, 2013 6:47 pm

CRail wrote:
boblothrope wrote:
CRail wrote:Many of the delays, slow downs, and hold ups on the red and orange lines are caused by automatic operation.

No, they're caused by poorly designed block lengths and locations, and bunching at chokepoints (slow crossovers at terminals, and the crowded downtown stations)...

Choke points: Havard Curve, where the train is limited to 10mph until well clear of the curve, and then several times afterwards when the code continues to fluctuate. That's an automatic operation slow down which manual operation wouldn't have.

Junctions: Approaching Ashmont, if a train is lined into the southbound lead, it receives a proper code into the station. If it is lined to cross over to the northbound lead and change ends (which is more common), it receives a 25 (approx) code from a short way south of Shawmut Ave. all the way into Ashmont. This wouldn't occur with Manual operation.


Again, those aren't specific to automatic operation. You are describing problems in the block configuration, which is independent of automatic or manual operation.

There's the basic safety issue: How fast can a train go on a stretch of track, considering the curve geometry, switch lineup, and trains ahead? The designers of the signal system decide what those speeds are, and the signal system communicates it to the person or computer driving the train.

If the signal system enforces slow speeds for longer stretches of track than are necessary for safety, it's a waste of potential capacity. It doesn't matter if a motorman sees the 10 mph speed code, or an automatic train-driving system sees it. (Unless you're advocating that motormen should decide for themselves if it's safe to go faster than the signal system tells them to, which is a terrible idea.)

The Red and Orange signal systems were replaced in order to allow automated operation. When that happened, the blocks were designed badly. But the problem isn't an automatic operation problem.

CRail wrote:
boblothrope wrote:They should leave the busier route green by default.

No, they shouldn't. You can't have a permissive signal drop, and you can't change a route once it has been established. That's rail safety 101. Heavy rail lines are centrally controlled, the green line is not.


Rail systems all over the world, including all of the MBTA's lines besides the Green Line, give permissive signals to the main line by default, and stop signals to approaching branch lines or conflicting crossover moves. When a train needs to use a conflicting route, the main line's signal would drop, *if* it was safe to do so (no approaching trains on the main).

No central control is necessary for this, though central control could be helpful on the Green Line for other reasons.
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Re: Public meeting on Green Line issues on 1/17/13

Postby CRail » Thu Jan 24, 2013 11:22 pm

I'm not interested in going back and forth repeating the same things over and over again. People who remember both lines prior to ATO talk about how the lines moved much more rapidly then. The running time from Park St. to Harvard in the Boston Elevated days was 7 minutes. There may be other factors which contribute, but ATO is certainly a big one. ATO speed zones also are bound to block limits, whether or not one approves of their locations, where as speed restriction boundaries without ATO can be fluctuated to the specific area where it's necessary, and only in that area. Plus, the Blue Line runs without ATO and, other than the potential wire problems, you seldom hear of any issues over there. There are speed control and positive stop mechanisms in place which instill safe operation without the headaches of automation (and the block lengths DON'T ruin the world). Regardless, the T has decided (thankfully) that a computerized system would be too expensive and costly to the service's efficiency to be feasible. Moving. Right. Along.

The heavy rail lines and railroads do not default routes, they're set up by the Dispatcher. Signals can be "fleeted," which means it automatically resets once the block is cleared, but the junctions don't give priority without a human telling them to. I misspoke before, you CAN take a signal away, but you DON'T, and you certainly don't make it a standard operating procedure. Green line junctions have no such human control, and therefor do not default to permissive signals. The T has determined that the safest thing to do at these junctions is require a stop every time you get to one, and I agree with them. It prevents a signal from dropping before a car, it prevents complacency because a signal might usually be green, and in the event of a car's failure to stop, all opposing movements have stopped minimizing the chances of a collision. And it does so without the adverse affects of computerized operation, whether or not you're willing to accept they exist.
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