Alewife track maps?

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Alewife track maps?

Postby mjbellantoni » Thu Mar 05, 2015 3:30 pm

Hello All,

I'm interested in writing a simple simulation of traffic coming in and out of Alewife station. I want to see what the evening rush hour wait times outside of Alewife would look like if it had been built with three tracks and not two. (Or perhaps even a loop configuration.)

Does anyone know where I can find pointers to information about the tracks leading into Alewife? In particular, I'm trying to find out how many signal lights there are between Davis and Alewife, what the timing rules are for them and such. Is this information publicly available anywhere?

Many thanks!

-m
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Re: Alewife track maps?

Postby Gerry6309 » Fri Mar 06, 2015 9:13 am

mjbellantoni wrote:Hello All,

I'm interested in writing a simple simulation of traffic coming in and out of Alewife station. I want to see what the evening rush hour wait times outside of Alewife would look like if it had been built with three tracks and not two. (Or perhaps even a loop configuration.)

Does anyone know where I can find pointers to information about the tracks leading into Alewife? In particular, I'm trying to find out how many signal lights there are between Davis and Alewife, what the timing rules are for them and such. Is this information publicly available anywhere?

Many thanks!

-m

There is an interlocking and scissors crossover at each end of the Davis-Alewife block, with a maximum speed of 40mph between them. Trains are slowed to 25 or 10 when being crossed over, and are stopped if both tracks in Alewife are occupied. Max capacity is one train in each direction.

A train leaving Alewife on the "normal" southbound track can run at track speed into Davis, where it has to slow to 25.

Any other move is slower.

There are two interlocking signals in each direction, everything else is electronic.
Gerry. STM/BSRA

The next stop is Washington. Change for Forest Hills Trains on the Winter St. Platform, and Everett Trains on the Summer St. Platform. This is an Ashmont train, change for Braintree at Columbia.
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Re: Alewife track maps?

Postby CRail » Fri Mar 06, 2015 11:54 am

Image

I like visuals, so I provided a track schematic so you can see what Gerry is talking about (schematic = NOT to scale, but characteristically correct). What I don't know is how many blocks exist between Davis and Alewife. The number of blocks determines how many trains can fit between the two stations on a given track (trouble is you can't see them). Wayside signals only exist at interlockings to provide indication of a lined and cleared routing, block signals ("Automatics") are in the form of cab signals which limit the train's speed automatically. If the interlocking is "reversed", that is, if the train is going to cross over, the "distant signal" (which doesn't actually exist in the form of a fixed signal as it is a "bond" in the gauge that controls the ATO) will transmit a 25 code or 10 code depending on the rating of the crossover (speed at which trains can safely travel through switches).

The junction just south of Alewife, while controlled by the OCC Dispatcher, operates automatically. It defaults to the Southbound track if it's not occupied. This way a train is crossed ahead of time and can begin its next trip without delay. This also allows the train to depart without tying up the interlocking if a Northbound train is approaching. In this situation, and only this situation, trains can depart and arrive simultaneously. It's impossible to allow a train to arrive on the southbound track and depart on the northbound track simultaneously (I suppose 'impossible' is a strong word since, theoretically, if you crossed trains at Davis and ran both trains wrong iron in both directions this could be done, although it would have to be done 'on the bypass' as the ATO would not allow it).

Another worthy piece of information, is that a train lined into a station track following a train laying up in the yard will not be allowed over the interlocking until the train laying up is completely to the north of the station track. Again, I don't know exactly where that bond is so I'm unsure of the exact timing. It's common, however, for a train to be stopped south of Alewife because a train going into the yard hasn't yet cleared the station.
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Re: Alewife track maps?

Postby boblothrope » Fri Mar 06, 2015 2:58 pm

CRail wrote:What I don't know is how many blocks exist between Davis and Alewife.


My educated guess is 3. I've learned that if a northbound train is parked on the left-hand curve, it's waiting for the last signal before the Alewife crossover. A bit before that and it's two signals away. If it stops just after the Davis crossover, it's three.

If a train is waiting for the northbound Davis crossover signal, the front half of the train will be sticking onto the platform. I have no idea why they couldn't design this better, so a train could do its station work while it waits for the signal. Tweaks like that make all the difference between a smooth rush hour and stop-and-go traffic.
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Re: Alewife track maps?

Postby Gerry6309 » Fri Mar 06, 2015 9:44 pm

boblothrope wrote:
CRail wrote:What I don't know is how many blocks exist between Davis and Alewife.


My educated guess is 3. I've learned that if a northbound train is parked on the left-hand curve, it's waiting for the last signal before the Alewife crossover. A bit before that and it's two signals away. If it stops just after the Davis crossover, it's three.

If a train is waiting for the northbound Davis crossover signal, the front half of the train will be sticking onto the platform. I have no idea why they couldn't design this better, so a train could do its station work while it waits for the signal. Tweaks like that make all the difference between a smooth rush hour and stop-and-go traffic.

Those blocks are only used for speed control. A train will be held at the interlocking signal leaving Davis (rear still in the station) until the Alewife interlocking is clear.

JFK to North Quincy may be the only stretch where more than one train is allowed between stations. Compare this to the old days when between Broadway and South Station a following train could approach the channel curve, being held on the superelevation, and getting a yellow as soon as the train ahead tripped the first signal on its way to Washington. His follower could get a yellow out of Broadway and could clear the platform!
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Re: Alewife track maps?

Postby mjbellantoni » Sat Mar 07, 2015 10:27 am

Wow. Thank you very much for so much information and for an incredibly helpful schematic! I'm going to collect some real time data over the next week and see if I can identify the actual location of the interlocks and the blocks (if I have that terminology correct.) I'll report back on whether I was able to do that successfully or not.

I'm wondering now what a hypothetical three-rail (two-platform) Alewife station would look like. I'm thinking that the the track layout used in the yard to the north of the actual station would be a reasonable arrangement? Something like this:

Image

Thanks again for all the help!

-m
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Re: Alewife track maps?

Postby BostonUrbEx » Sat Mar 07, 2015 4:22 pm

For maximum movement, you'd want one of the options I've added to this post.
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Re: Alewife track maps?

Postby The EGE » Sat Mar 07, 2015 5:05 pm

For any of those, you want the ability to reverse trains on tail tracks past the platforms. That way, a train on the far northbound platform track can return southbound without blocking all trains from entering the station. In this configuration, the top platform serves all outbound trains, and the bottom platform all inbound trains.

alewife1.PNG
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The existing configuration, with a connector from the northbound track to the pocket track, would have been perfect for an extension to Arlington. Easy way to short-turn trains.
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Re: Alewife track maps?

Postby boblothrope » Mon Mar 09, 2015 1:32 am

Gerry6309 wrote:
boblothrope wrote:My educated guess is 3. I've learned that if a northbound train is parked on the left-hand curve, it's waiting for the last signal before the Alewife crossover. A bit before that and it's two signals away. If it stops just after the Davis crossover, it's three.

Those blocks are only used for speed control. A train will be held at the interlocking signal leaving Davis (rear still in the station) until the Alewife interlocking is clear.


I really doubt that. I've been on a *lot* of outbound trains which stopped for several minutes on the left-hand curve just before the Alewife interlocking, staring at my watch hoping I'll make my bus connection. Then right after I hear the inbound train pass, we move across the interlocking and through the right-hand curve, into the station.
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Re: Alewife track maps?

Postby mjbellantoni » Mon Mar 09, 2015 6:06 am

boblothrope wrote:I've been on a *lot* of outbound trains which stopped for several minutes on the left-hand curve just before the Alewife interlocking, staring at my watch hoping I'll make my bus connection.


I am in the same boat. I came up with the idea for this project while sitting in the tunnel waiting for a berth to open as my bus happily left without me.

It does seem like there are multiple stopping point between Davis and Alewife and not just at the interlockings. I'm now actively collecting data from the real time feeds. Hopefully, I will have something to share in a few days.
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Re: Alewife track maps?

Postby Gerry6309 » Mon Mar 09, 2015 11:39 pm

Three is the magic number. All trains are separated by three full signal blocks. Thus if there is a train stopped at the Alewife interlocking, his follower has to wait at Davis interlocking. You can't approach your leader closely unless the blocks are VERY short. Think Park to Downtown Crossing.
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Re: Alewife track maps?

Postby mjbellantoni » Tue Mar 10, 2015 10:19 am

Gerry6309 wrote:Three is the magic number. All trains are separated by three full signal blocks. Thus if there is a train stopped at the Alewife interlocking, his follower has to wait at Davis interlocking. You can't approach your leader closely unless the blocks are VERY short. Think Park to Downtown Crossing.


So I understand, "signal block" is equivalent to "interlocking." Is that correct? Further, there are other, unmarked points within the blocks where a train may receive a signal to change its speed to 10 MPH or 25 MPH (or even stop?)

Thanks again for the education!

-m
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Re: Alewife track maps?

Postby dbperry » Tue Mar 10, 2015 10:34 am

just found that great schematics for all subway lines are in the Blue Book:

http://www.mbta.com/uploadedfiles/docum ... dition.pdf

http://www.mbta.com/about_the_mbta/docu ... ch+Library

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Re: Alewife track maps?

Postby CRail » Fri Mar 13, 2015 1:49 am

mjbellantoni wrote:So I understand, "signal block" is equivalent to "interlocking." Is that correct? Further, there are other, unmarked points within the blocks where a train may receive a signal to change its speed to 10 MPH or 25 MPH (or even stop?)

You sort of answer yourself here. Look at my track diagram above. The things which are protected by the only signals you see are interlockings. Basically, any location on the main line where something different can happen (I can go left or right...) is an interlocking. Blocks are the other unmarked points where a train may receive a signal to change speed or (yes, even) stop. Conventionally, blocks are protected by wayside signals. On the blue and green lines, you can tell where each block ends because there's a signal at their boundaries. On the red and orange lines, which have ATO, the only wayside signals are at interlockings which my diagram reflects. Other signals are invisible (except you can see the "bond" in the gauge if you're the motorman or walking the track) and control the cab indication and speed code.

boblothrope wrote:I've been on a *lot* of outbound trains which stopped for several minutes on the left-hand curve just before the Alewife interlocking, staring at my watch hoping I'll make my bus connection.

You're talking about trains operating in the opposite direction clearing a station track for a northbound arrival. Naturally, if there is a train crossing over from the northbound to the southbound track, the northbound train can't proceed past the interlocking until it's clear. That's not what Gerry was talking about. A northbound train leaving Davis Sq. cannot proceed past the interlocking north of the station until the northbound ahead of it has cleared the interlocking south of Alewife (this is a clarification of the point, I don't know this to be true except that if Gerry says so it probably is). This has nothing to do with southbound movements.
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Re: Alewife track maps?

Postby Gerry6309 » Fri Mar 13, 2015 7:01 am

Let's assume that we have a train waiting for a terminal track at Alewife. The interlocking signal at the switch is red over red: Stop and Stay: No Route. The next block behind the signal is also at stop as a protective measure, thus the train is waiting 800 feet short of the interlocking. The block occupied by the train is at stop for obvious reasons. plus the two blocks following are also at stop. The fifth block from the signal will be at approach: 600 feet of 25 code and 200 feet of 10 code. This spacing carried over from the old wayside system between Harvard and Ashmont. Block length varied, for example, there were three signals southbound between Park and Washington. All three would be red if the platform at Washington was occupied. This practice was used on all rapid transit lines. On the Green Line, a block clears to approach as soon as it is vacated, allowing for the typical tight headways.
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