What does a yellow light mean?

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What does a yellow light mean?

Postby Yellowspoon » Wed Jul 08, 2015 8:25 am

Reverend Jim Ignatowski knows.

Is there a speed limit when operating under a yellow light? Last night there was a disabled train outbound on the D line and a few trains were backed up. We waited at several red lights. As each red light turned yellow, the operator would go at full speed to the next red light. About 1/2 mile before Newton Center there was one red light hiding behind vegetation. It caused the operator to brake harder than normal when she finally saw it. It came close to an emergency stop.

And while I'm on the subject of yellow lights ... On the orange line between North Station and State, in each direction are yellow-over-red signals (or red-over-red after a train passes). What are these for? Is there a crossover between the stations?

The photograph shown is merely illustrative. The vegetation in front of this signal has been removed.
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Re: What does a yellow light mean?

Postby jboutiet » Wed Jul 08, 2015 9:31 am

This doesn't directly answer your speed limit question, but it explains the meaning of the signals:

http://www.nycsubway.org/wiki/MBTA_Gree ... ne_Signals
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Re: What does a yellow light mean?

Postby Disney Guy » Wed Jul 08, 2015 12:20 pm

The plain (single circular) yellow light on the Green Line has the standard meaning as on three aspect block signals on most U.S. railroads nationwide.

When the operator saw the following signal red and almost hidden behind a bush, he had to make a panic stop, it was a combination of proceeding at too great a speed and an imperfect indication (obstructed view) from the red signal.

Nothing prevents the operator from reaching or proceeding at fulll speed past a plain yellow indication and then making a quick although still comfortable stop at a red signal following. But this is somewhat energy inefficient compared with proceeding at a lesser speed if the train reached the next signal that was still red.

Green Line subway stations have always (at least since the 1950's) been separate blocks where the signal at the station entrance changed from single red to double yellow when space opened up behind an entering train. A long time ago, double yellow permitted entering the station on the fly but under line of sight control to stop immediately behind a train already in the station. The operator had to use discretion, not entering the station more than one car length with a 3 car train that could not enter completely, for fear that the conductor of the second car might open his doors. Following some collisions in the late 20'th century due to carelessness or inattention by operators, a full stop is now required at the double yellow signal.

"Proceed prepared to stop at next signal" can also apply to yellow arrows at facing switches and plain yellow at trailing switch interlocking although track conditions (curves, special work) call for lower speeds. It is not unusual for a signal immediately after a trailing switch to show red as a car receives a yellow just prior to the switch and then proceeds.
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Re: What does a yellow light mean?

Postby highgreen215 » Wed Jul 08, 2015 4:11 pm

I think you should report that hidden signal to the MBTA - surprised if trolley operators have not already done so. You could be preventing a possible tragedy.
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Re: What does a yellow light mean?

Postby Gerry6309 » Wed Jul 08, 2015 4:41 pm

In cab signal territory, it simply indicates the condition of the interlocking, or the track to the next station if there is no interlocking. Cab signal governs speed.
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Re: What does a yellow light mean?

Postby dieciduej » Wed Jul 08, 2015 4:47 pm

From what I can remember about signal colors on the Light Rail Lines:

Interlocking: Yellow - Proceed at 6 MPH.

Automatic Block & Traffic Control: Yellow - Proceed and be prepared to stop at the next signal.

The Orange Line signals between Haymarket and North Station are for the crossover. Yellow over Red (Normal Route), Red over Yellow (Diverging Route). Signals between Haymarket and Downtown Crossing are more for information due to line-of-sight issues, the tracks taking take a dip NB and the curve into State SB.

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Re: What does a yellow light mean?

Postby CRail » Thu Jul 09, 2015 12:09 pm

Yellowspoon wrote:On the orange line between North Station and State, in each direction are yellow-over-red signals (or red-over-red after a train passes). What are these for? Is there a crossover between the stations?

The only wayside signals on the Red and Orange lines are at junctions, everything else is handled by the cab signal/ATO system. Yellow over Red means the facing switch in the junction is normalized, Red over Yellow means the switch is reversed. Red over Red naturally is a stop signal, a route past it has not been established.
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Re: What does a yellow light mean?

Postby bostontrainguy » Tue Jul 14, 2015 9:26 am

Yellowspoon wrote:Reverend Jim Ignatowski knows.

Is there a speed limit when operating under a yellow light?


No, only indicates that the next signal is (usually) red and the driver must be prepared to stop at that signal.
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Re: What does a yellow light mean?

Postby Yellowspoon » Tue Jul 14, 2015 7:26 pm

dieciduej wrote: ... Signals between Haymarket and Downtown Crossing are more for information due to line-of-sight issues, the tracks taking take a dip NB and the curve into State SB.
JoeD
What "information" are they passing on to the train operator? Do you have a cite for that because it doesn't sound logical. The MBTA is so old that dips and curves are all over the place. To my knowledge, the only yellow-over-red signals that do not approach a switch occur between Downtown Crossing and Haymarket. In the case of Haymarket, the south end of the station has north facing yellow-over-red signals on both northbound and southbound tracks.

bostontrainguy wrote:
Yellowspoon wrote:Is there a speed limit when operating under a yellow light?

No, only indicates that the next signal is (usually) red and the driver must be prepared to stop at that signal.
The signal at the west end of Waban (westbound) never turns green. I assume this is a result of the accident of 28-MAY-08. What you're saying is that it has no meaning.

Separately ... the signal at the north end of track 3 at Park Street is usually green. Is there an intervening yellow in the 20m before the switch from Government Center, or can a BC train go from green directly to (double) red?
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Re: What does a yellow light mean?

Postby CRail » Tue Jul 14, 2015 11:48 pm

Yellowspoon wrote:The signal at the west end of Waban (westbound) never turns green...What you're saying is that it has no meaning.

No, it indicates to the motorman that he/she must operate the train prepared to stop at the next signal. There are several signals which never turn green regardless of the following signal's aspect, being prepared to stop doesn't mean that you're going to.
Yellowspoon wrote:Separately ... the signal at the north end of track 3 at Park Street is usually green. Is there an intervening yellow in the 20m before the switch from Government Center, or can a BC train go from green directly to (double) red?
Yes there is. If everything is working properly, you will never get a green before a red, double red, or double yellow.
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Re: What does a yellow light mean?

Postby bostontrainguy » Wed Jul 15, 2015 10:03 am

CRail wrote:
Yellowspoon wrote:The signal at the west end of Waban (westbound) never turns green...What you're saying is that it has no meaning.

No, it indicates to the motorman that he/she must operate the train prepared to stop at the next signal. There are several signals which never turn green regardless of the following signal's aspect, being prepared to stop doesn't mean that you're going to.
Yellowspoon wrote:Separately ... the signal at the north end of track 3 at Park Street is usually green. Is there an intervening yellow in the 20m before the switch from Government Center, or can a BC train go from green directly to (double) red?
Yes there is. If everything is working properly, you will never get a green before a red, double red, or double yellow.


Believe it or not, there are some signals that can go from green immediately to double red. The most frequent occurrence of this is the signal just before the fence after the switch outbound between Beaconsfield and Reservoir. If the crossover is thrown at the Reservoir station while a train is approaching the green signal at this point, it will turn double red and trains will unavoidably violate the signal.

I also have to take issue with the practice of signals that never turn green. The one that really bothers me is the one just before the curve westbound after Brookline Hills. Again, due to an accident here many many years ago, the signal was added and set to only allow a yellow indication. So every time a driver approaches that curve, the signal is yellow and the next "blind" signal around the bend is usually always green. Human nature is to expect that. However, some day a train is going to break down just after that second signal and a train going westbound at 40 mph is going to round that curve and not be able to stop. I think it's safer not to have these false indications and have signals that show the actually situation. If that signal is usually green, and one day it happens to be yellow, the operator knows that the next signal is red and will prepare to stop. If a signal is always yellow, operators tend to become complacent. I think the practice is not safer but actually more dangerous.
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Re: What does a yellow light mean?

Postby ExCon90 » Wed Jul 15, 2015 2:18 pm

There has been more than one collision on main-line railroads arising from exactly that situation. About the only fail-safe way I know of to guard against that is the white light below the yellow used by NYCTA to indicate that it's a speed-control signal and will clear up if the train is not exceeding the prescribed speed. The absence of white where it would normally be shown tells the operator that this time it's not the speed--he really needs to be prepared to stop. That could be arranged here by adding a white signal below the yellow; the absence of white would indicate that there really is a car ahead, while the presence of the white would indicate that it's only necessary to observe the speed restriction without being concerned about a car ahead.
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Re: What does a yellow light mean?

Postby Disney Guy » Wed Jul 15, 2015 7:30 pm

I could expect that there may be manually operated switches where an interlocking signal displays green for the primary direction of travel and interlocking is nonresponsive to conflicting movements.

No one is supposed to throw the switch or change the interlocking mode before making sure that no train is approaching. For the Green Line, if the interlocking were put in automatic mode or the switch pegged for an adverse movement then the signal just preceding the switch and for the previously favored movement should display double red.

Backing up a train in signalized territory will also cause uncanny signal indications to appear in view of trains moving in the normal direction. Every well run railroad has procedures, many involving sending a flagperson on foot, to protect an adverse movement against approaching trains.

On the Green Line operators should not become complacent about a signal that rests in yellow while the next signal is usually green. Even the Riverside line backs up reasonably often and the operator will find the next signal red (or yellow).
Last edited by Disney Guy on Wed Jul 15, 2015 8:19 pm, edited 1 time in total.
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Re: What does a yellow light mean?

Postby Yellowspoon » Wed Jul 15, 2015 8:05 pm

CRail wrote:
Yellowspoon wrote:The signal at the west end of Waban (westbound) never turns green...What you're saying is that it has no meaning.

No, it indicates to the motorman that he/she must operate the train prepared to stop at the next signal. ...
It doesn't answer the question. Why is this signal different? If this yellow light means to be prepared to stop at the next signal, why not eliminate green and only use yellow/red for all signals?

From a different point, if the signal is always yellow, the operator will assume it is false and treat it as a green. As an example: There is a red signal between Kenmore & Hynes inbound. Once or twice a year, the operator will blow through that signal because he assumes that the track ahead is clear. So far, he/she has always been right.
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Re: What does a yellow light mean?

Postby CRail » Wed Jul 15, 2015 11:02 pm

Your question was answered. You asked if it meant the signal had no meaning, and that was incorrect. It means that the motorman is to approach the next signal assuming that it is going to be red. Regarding the block signals that are always red, those are called time lights, there are several. Whether or not you agree with the practice is irrelevant to its reasoning.

Observance of signals is not a topic for discussion here and I doubt you have an accurate count of how many violations might occur per annum.

In regards to a green to a red, this is designed not to happen. In the railroad world, manually operated switches on signaled main lines will not unlock if there is a route cleared over them, and even after they are unlocked they must not be thrown sooner than whatever the rulebook prescribes (I think NORAC says 5 minutes but I might be wrong). Back to the green line, there was discussion before on here about signals that are always red, including at junctions. THIS is exactly why junctions always show double reds in all directions, so that a signal never drops in the face of an approaching train.

In my own personal opinion, I do agree that a light never upgrading to green even when the following signal is green is bad practice. Also, it was pointed out to me that many of the time lights, which exist to enforce speed, do not clear in the amount of time it takes to approach the signal at the appropriate speed. This means that trains have to stop at the signal despite the fact that track speed was never exceeded. This I also don't agree with, although I assume it's so that the motorman of a train will stop regardless and not assume it will clear up upon approach. The way to deal with this (as was already explained above) is to have the previous signal yellow over white, the white indicating that the only reason the next signal is red is that it's holding time. This occurs on the blue line. If you have a yellow over white, maintain track speed and the signal will clear when you get to it. If it's just yellow, prepare to stop.
Last edited by CRail on Thu Jul 16, 2015 6:41 am, edited 1 time in total.
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