Could someone explain

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Could someone explain

Postby Yellowspoon » Mon Mar 14, 2016 10:31 am

(1) About halfway between Downtown Crossing and State (orange line northbound), there is a yellow-over-red signal. What does it mean? There is no diverging route anywhere near here.

(2)I see several white lights. I've noticed them on the Red & Orange lines. They're behind a fresnel lens, so they signal something. They usually face away from the oncoming trains, like the one in the picture below. The below photograph was taken at Charles facing Park Street. Based on my observations, the light is ON most of the time. When the light turns off, a train arrives at from Park Street abour two minutes later. The light remains OFF while the train is in the station, but turns ON before the train has completely left the station. And the cycle repeats. All the other lights of this type have a similar behavior. Inquiring minds want to know.
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Re: Could someone explain

Postby jwhite07 » Mon Mar 14, 2016 10:55 am

Can't recall the answer to the first one off the top of my head, but I'm sure someone else will know.

The second signal is a train approach indicator. It is used to warn work crews of approaching trains. Indeed, the light is lit except when a train is approaching, at which time it turns off, which serves as the warning. Seems backwards, but it is a built in fail-safe. If the light burns out, a work crew should treat it the same way as a train approaching and get clear.
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Re: Could someone explain

Postby CRail » Mon Mar 14, 2016 10:34 pm

If your picture went just slightly to the right, you'd see another signal just like it. It's only capable of showing yellow over red and red over red. It's just a redundant signal in a location they apparently wanted a wayside in addition to the ATO/cab signal system.
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Re: Could someone explain

Postby dieciduej » Tue Mar 15, 2016 1:56 am

I am not sure if there is a proper name for the, yellow over red, signal, but I call it a repeater signal. Even though the trains are ATO/Cab Signaled there is the chance that a train maybe on bypass, ala Braintree incident. This gives the train operator a sense of what is ahead of the train. You will see these signals where line-of-sight is obscured, in your example the trackage dips and curves between Downtown Crossing and State northbound. In the photo of Charles St a curve into a portal. There is one on the Orange Line southbound about 50 yards into the portal. One thing to mention these signal are just indicators and do not have any safety hardware, aka a trip arm, to stop the train if someone passes the double red.

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Re: Could someone explain

Postby Yellowspoon » Tue Mar 15, 2016 8:38 am

I don't think either of my questions have been completely answered.

With the issue of the white light ...

jwhite07 wrote: ... The second signal is a train approach indicator. It is used to warn work crews of approaching trains. Indeed, the light is lit except when a train is approaching, at which time it turns off, which serves as the warning. Seems backwards, but it is a built in fail-safe. If the light burns out, a work crew should treat it the same way as a train approaching and get clear.
Yes, the light tells of an approaching train, but it can hardly serve as a warning. Unlike interrupt warnings (bells, vibration, strobes), one must make a conscientious effort to keep watching the light to see when it turns off. In addition, these only appear in a handful of places. If they were for warnings, workers could be anywhere on the system so there should be multiple white lights throughout the system. I don't see any of these on the green line. (I don't use the blue line often enough to notice).


With regard to the yellow-over-red between Downtown Crossing and State on the northbound orange line, this is the only yellow/red combination (of which I know) that does not indicate the status of a facing switch.
CRail wrote:If your picture went just slightly to the right, you'd see another signal just like it. It's only capable of showing yellow over red and red over red. It's just a redundant signal in a location they apparently wanted a wayside in addition to the ATO/cab signal system.
Are you sure? I believe the yellow-over-red light at Charles indicates to proceed to track 5 at Park. Although I've never seen it, I believe the light could turn red-over-yellow to show that the train should take the crossover and proceed to track 6 at Park Street. Back when they used to turn some Quincy trains at Park, the northbound operator would receive a red-over-yellow to indicate (s)he should take the diverging route to track 5 for a southbound journey.

dieciduej wrote:I am not sure if there is a proper name for the, yellow over red, signal, but I call it a repeater signal. Even though the trains are ATO/Cab Signaled there is the chance that a train maybe on bypass, ala Braintree incident. ... JoeD
I believe (but I'd be happy to hear otherwise) that the Braintree incident only overrode the dead-man's feature and one (and only one) signal. I belive the train would have stopped via ATO before hitting the train in front or upon hitting a red-over-red. Cutting the power simply emiminated an emergency stop and/or a ride all the way to Alewife. If that's not the case, then the MBTA needs to revisit their handling of emergencies and ATO.
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Re: Could someone explain

Postby MBTA3247 » Tue Mar 15, 2016 8:59 am

Yellowspoon wrote:
jwhite07 wrote: ... The second signal is a train approach indicator. It is used to warn work crews of approaching trains. Indeed, the light is lit except when a train is approaching, at which time it turns off, which serves as the warning. Seems backwards, but it is a built in fail-safe. If the light burns out, a work crew should treat it the same way as a train approaching and get clear.
Yes, the light tells of an approaching train, but it can hardly serve as a warning. Unlike interrupt warnings (bells, vibration, strobes), one must make a conscientious effort to keep watching the light to see when it turns off. These only appear in a handful of places. Workers could be anywhere so there should be multiple white lights throughout the system.

The white lights are for the benefit of track inspectors, who would be walking down the track opposite the direction of traffic looking for any visible issues. The lights are only needed at curves or other locations where visibility is restricted; the rest of the time, the inspectors can see trains approaching, so there's no need for a dedicated warning system. If a maintenance crew was actually doing work on the tracks, there would be additional protective measures in place (the big one being that such work is usually done at night when the system is shut down).

I believe (but I'd be happy to hear otherwise) that the Braintree incident only overrode the dead-man's feature and one (and only one) signal. I belive the train would have stopped via ATO before hitting the train in front or upon hitting a red-over-red. Cutting the power simply emiminated an emergency stop and/or a ride all the way to Alewife. If that's not the case, then the MBTA needs to revisit their handling of emergencies and ATO.

The operator switched off the train's ATO receiver to operate it in bypass mode. With the deadman also compromised, that train wasn't going to stop until either the power was cut or it hit something.
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What are these rumble strips for?

Postby Yellowspoon » Sun Mar 27, 2016 5:48 am

This photo was taken at the new GC station. The track on the left loops back to Haymarket and the unseen track to the right also goes to Haymarket. What is the purpose of these white rumble strips? They're about 300mm (1 foot) wide and about 18mm (3/4") high. There are two gaps in each rumble strips, each gap is about 1m (3 ft) from each track.
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Re: Could someone explain

Postby BostonUrbEx » Sun Mar 27, 2016 8:39 am

They're for the blind to feel out where they should wait for a train and where the doors *should* be lined up at the platform.
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Re: Could someone explain

Postby dieciduej » Sun Mar 27, 2016 3:45 pm

As it was explained to me they are to mark the customer assistance area. This is the area where the emergency call box are located. You will find them on most platforms now. I am not sure of there usefulness.

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