Can dispatcher specify aspect of absolute signal?

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Can dispatcher specify aspect of absolute signal?

Postby dbperry » Tue Dec 08, 2015 9:51 am

This question is specifically about the non-cab signaled Framingham to Boston section of the ex-B&A line, but feel free to answer for other systems / lines.

Understanding that a dispatcher can neither see nor control the automatic signals, can a dispatcher specify the aspect of an absolute signal at an interlocking? Put another way, if a dispatcher lines the switches so that a train can proceed through an interlocking, is the signal aspect then automatically displayed according to the block or interlocking 'program' or 'rules?' Or could the dispatcher align the switches such that the train should / could see a clear signal, but the dispatcher manually changes it to slow clear (or something else) to run the train slower (for some operational reason)?
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Re: Can dispatcher specify aspect of absolute signal?

Postby MBTA F40PH-2C 1050 » Tue Dec 08, 2015 11:04 am

No....the Dispatchers upstairs can not see what Aspect is displayed in the field....For them, at an Interlocking or a CP, the signal on their screen that they see is either a RED or GREEN bulb....and they can't see the automatics on their screens upstairs...I'll try to get a picture and post on NERAIL at some point of their screen.just so you can see what they actually see....but it is a bunch of white lines, green lines are paths lined up for trains, red in a portion of a block indicates a train, or something shunting the circuit and red and green bulbs at INT's or CP's... What they see This is as accurate as I could find for right now on the web
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Re: Can dispatcher specify aspect of absolute signal?

Postby dbperry » Tue Dec 08, 2015 11:45 am

That's easy! Here's a picture. I didn't realize this was the same as dispatchers see. This picture is really old (there's even something spotted on the Herald siding!), but it sounds like same story...

http://photos.nerail.org/showpic/?photo ... ey=dbperry
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Re: Can dispatcher specify aspect of absolute signal?

Postby MBTA F40PH-2C 1050 » Wed Dec 09, 2015 1:58 am

perfect! yes, that is the South Station area as you already know, and that was the old system before the new CTEC got remodeled upstairs....With this picture that you provided I'll answer more of your questions....I assume you are familiar with the Corridor/Mainline. If you look at the screen, you'll see COVE and PLAINS interlocking...that purple square shows a station on their screen, but as you may know, there is Back Bay and Ruggles station between those two interlockings but only one station shows on the screen. Only so much can be shown on their screens. There is also the Automatic signal...226.1/226.2 just after Ruggles station going Westbound, which if you look closely is "shown" as a cut in the line behind AMTK 160....so they are there
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Re: Can dispatcher specify aspect of absolute signal?

Postby Rockingham Racer » Wed Dec 09, 2015 6:46 am

When a call-on, restricting signal is set by the dispatcher, what's on the board in terms of the color of the signal icon?
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Re: Can dispatcher specify aspect of absolute signal?

Postby BostonUrbEx » Wed Dec 09, 2015 7:07 am

Any signal that is in is green. Restricting, Approach, Clear, Slow Approach, Limited Clear, Medium Approach Medium, Snail Approach Cheetah, all the same.
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Re: Can dispatcher specify aspect of absolute signal?

Postby dbperry » Wed Dec 09, 2015 9:42 am

i was thinking that maybe dispatchers could 'click' on an individual signal at an interlocking and either get more detailed info about it or be able to 'adjust' it. Like in a popup window or separate screen on the computer or something.

Thanks for teaching us!
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Re: Can dispatcher specify aspect of absolute signal?

Postby DutchRailnut » Wed Dec 09, 2015 10:07 am

the Dispatcher has no idea what aspects shows.
Dispatcher or a tower operator only has board showing occupied/free /locked out.
when operator sets a route, he/she clicks in and out button for that interlocking.
The interlocking electronics do rest, they set requested switches and set appropriate indication in field for that route, based on max speed for certain turnouts and based on track occupancy.
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Re: Can dispatcher specify aspect of absolute signal?

Postby ns3010 » Wed Dec 09, 2015 12:16 pm

What about control points without an interlocking? (Do any of these even exist on the T?) The signals can't be based on a route lining since there's no route to be lined, so they would have to be go/don't go based on track occupancy. I would think there needs to be some way that the dispatcher could set the home signal, otherwise it would just be another automatic.
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Re: Can dispatcher specify aspect of absolute signal?

Postby BostonUrbEx » Wed Dec 09, 2015 1:05 pm

It doesn't matter, under no condition can a dispatcher see or adjust a signal aspect, whether it be an interlocking, a control point, or an automatic. That could potentially be very dangerous as the system has already maximized the signal for the conditions as is. In addition, a dispatcher cannot tell a train what proceed indication is up ahead, nor should a train act upon that information if it is given. Trains are to follow the signal system as displayed.
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Re: Can dispatcher specify aspect of absolute signal?

Postby 8th Notch » Wed Dec 09, 2015 1:15 pm

ns3010 wrote:What about control points without an interlocking? (Do any of these even exist on the T?)


Yes they do exist on the T, its been awhile since I've been to Fitchburg but Martin St at S.Acton is one.
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Re: Can dispatcher specify aspect of absolute signal?

Postby ns3010 » Wed Dec 09, 2015 1:16 pm

Interesting, so the home signal of a non-interlocked control point just responds based on the occupancy/route of the blocks ahead, the same as an automatic? If it does respond the same as an automatic, then why would it be designated as a control point?

And yes, I forgot about Martin Street. Thanks!
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Re: Can dispatcher specify aspect of absolute signal?

Postby BostonUrbEx » Wed Dec 09, 2015 1:22 pm

If a Control Point acts as a distant signal to an Interlocking, it is possible they don't want trains stopped at the Interlocking itself or between the Interlocking and Control Point. There may also be scenarios, such as in freight territory, where headroom will be needed and in order to bring an opposing move towards that train in between Interlockings, you'll need Control Points.
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Re: Can dispatcher specify aspect of absolute signal?

Postby mvb119 » Wed Dec 09, 2015 6:04 pm

ns3010 wrote:Interesting, so the home signal of a non-interlocked control point just responds based on the occupancy/route of the blocks ahead, the same as an automatic? If it does respond the same as an automatic, then why would it be designated as a control point?

And yes, I forgot about Martin Street. Thanks!


It does not respond the same as an automatic signal, it responds to the dispatcher displaying the signal. Dispatchers cannot control an automatic signal. The main purpose of a CP signal without any switches associated with it is to use it as a holding signal so the dispatcher can stop a train and hold it there when necessary. Often times when they are not being used to hold trains, the dispatcher will fleet the signal. At that point it does basically act like an automatic signal in that the signal will restore itself once the train clears the block. This is not the same as an automatic because the dispatcher still has the ability to control it.

As to the original topic, dispatchers basically line the switches, the signal system does the rest of the work. It determines if the blocks ahead are occupied, and what speed the train should go through the interlocking. I've always thought the term controlled signal is a bit of a misnomer, since the system basically just sends the command to move the switches and then once they are lined and locked, the HSR (Home Signal Request) circuit gets activated, which is just the 1st step to displaying the signal. The system goes through 4 more steps almost instantaneously, but in essence it determines the route, then the block occupancy, and then finally the signal changes to the correct aspect. The dispatcher has no control over this because it is hardwired into the system for the proper speeds. If the dispatcher wishes to impose a slower speed, they can leave the signals at Stop and give the train permission past it at restricted speed.
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Re: Can dispatcher specify aspect of absolute signal?

Postby Trinnau » Wed Dec 09, 2015 8:51 pm

Martin St. has been gone for about a month now.

A control point without switches (like Martin St. was) is usually to protect a "headroom" move so that opposing traffic can operate operate toward a move on signal indication at track speed. Using the Martin St. example, the old interlockings at South Acton and Martin St were about a half a mile apart with the station platform at South Acton in the middle. The schedule dictated that some trains operated to South Acton, turned around and headed back in. In order to operate into the station at South Acton, a westward signal would be displayed at South Acton Interlocking but Martin St. could remain at Stop. If Martin St. didn't exist, the signal at South Acton would have cleared the block all the way to the Willows - setting westward traffic on the former single track for about 8 miles and not allowing an eastward move while a South Acton train turned around in the station. With Martin St. there, it allowed an eastward signal down the Fitchburg at the Willows to Martin St. while a train was turning in the station at South Acton.

With double track and turns extended to Littleton, Martin St. is no longer required.

A better example of this (not on MBTA territory) is CPF-244 in Dover, NH on the Pan Am Freight Main. This allows Pan Am freights to work the small yard and have headroom west from CPF-243 on the single track to CPF-244 without tying up the block for the next 12 miles to CPF-256. It takes a freight train roughly 25 minutes to cover that, so it is a way to keep opposing traffic moving.

There are other locations without switches - like Steeves in Ipswich or Slab City in Shirley - that are hold points so trains don't tie up crossings.
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