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Discussion Starter · #1 ·
For years I have observed the three light color signals on the old Reading, now SEPTA Railroad here in Southeastern Pa. As I was driving by the Glenside Station today, the signal just at the exit of the station was blinking green. What does this tell the engineer to do?
 

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I don't believe I ever saw a flashing green in my 30 yrs of RR service. I have seen a lot of flashing yellows which means that the next signal will be a solid yellow and the next red, so you better slow down your train. Possibly a flashing green is a signal malfunction or it might mean that the next signal will be a flashing yellow. I don't really know. BTW, was there possibly another light associated with the flashing green? Like a solid red or solid yellow? That would indicate that a diverging route was imminent.
 

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Some of the light rail systems use a flashing green to indicate a clear track on a diverging route, but I've never seen one on a "regular" railroad either.
 

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If I am driving on the highway, a flashing red means I have to stop before I can go... does a flashing green mean I have to go before I can stop?
 

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Discussion Starter · #6 ·
Posted By Semper Vaporo on 10/11/2008 7:01 PM
If I am driving on the highway, a flashing red means I have to stop before I can go... does a flashing green mean I have to go before I can stop?


Brilliant! Your sense of reason never astounds me. Why did I not think of that?
 

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Discussion Starter · #7 ·
Posted By Greg Stevens on 10/11/2008 12:50 AM
I don't believe I ever saw a flashing green in my 30 yrs of RR service. I have seen a lot of flashing yellows which means that the next signal will be a solid yellow and the next red, so you better slow down your train. Possibly a flashing green is a signal malfunction or it might mean that the next signal will be a flashing yellow. I don't really know. BTW, was there possibly another light associated with the flashing green? Like a solid red or solid yellow? That would indicate that a diverging route was imminent.


Not that I could see from the street.
 

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Discussion Starter · #8 ·
Posted By ohioriverrailway on 10/11/2008 11:16 AM
Some of the light rail systems use a flashing green to indicate a clear track on a diverging route, but I've never seen one on a "regular" railroad either.


I don't know if the SEPTA commuter trains are considered light rail. My guess is that they are not.
 

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In general a flashing aspect lets you display a signal that would require one more head than the signal it's on ... for example flashing yellow can replace yellow over yellow, or yellow over yellow over red (etc) ... so you can do "advance approach" on a single signal head.... you go from green, to flashing yellow, to yellow, to red .... and some systems modify it further by giving you flashing yellow, then yellow, then flashing red, then red: trains can pass the final flashing red at restricted speed. So the flashing light is often used to modify the signal one step in the "less restricting" direction.

Start wtih this:

http://broadway.pennsyrr.com/Rail/Signal/aspects_us_cl.html

So ... what does a flashing green give you? Most systems list this as "Cab Speed" .... but the above formula works. Think of it as Green over Green over red (over red...etc) where now you're clear to do whatever your cab signal tells you is allowed.... a speed that might be higher than ordinarily allowed at an interlocking or in block signal territory, where generally the signal only tells you what the next two blocks are like. Most of the time, block signal territory (where there is no cab signal equipment) is limited to 79MPH so you'll really only see the flashing green/ CAB SPEED indication where speeds over 80 are allowed. Notice the explanation in the NORAC signals:

http://broadway.pennsyrr.com/Rail/Signal/aspects_us_norac.html

So ... clear as mud?


Matthew (OV)
 

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Railroad signals actually came first ... the motor vehicle traffic kind were a simplified version. Signals generally tell you one of two things: 1.) The status of a block ahead of you (Occupied, as in, there's a train there, or Clear, as in, there's no train there) and 2.) Speed control (as in, "Slow down to Medium Speed as you pass this signal, and when you get to the next signal, be going slow enough that you can stop if it says to.")

Imagine a traffic light that told you "You can pass this signal at 45 mph, but be prepared to hang a left at the next light, and be going no faster than 10 mph when you get there!" You'd have a lot more than "Green, Yellow, Red" to remember ... and it might vary from state to state, or city to city.

The other thing that can be confusing about railroad signals is that red doesn't ALWAYS mean stop. Sometimes it's just a placeholder; sometimes it means "Stop and Proceed," and sometimes it means "Stop.. and stay stopped!" So, a two story tall "Green over Red over Red" is sometimes the LEAST restrictive signal in a system (and means "Clear") while a tiny dwarf signal with a red lamp might require a train to stop and wait indefinately for a better signal to be displayed!

The broadway limited pages are really good primer if you want to understand the basics of how most American signalling (and some from other countries) works, and how it came to be. The whole thing starts here:http://broadway.pennsyrr.com/Rail/Signal/index.html

Matthew (OV)
 

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Discussion Starter · #14 ·
When I drove by Glenside station today, I was able to see the signal more clearly. There is a red light on the disk below the one with the green flashing light.
 

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it just depends on the railroad. where i run on csx they use color light signals and a flashing green means limited clear. usually it is a red on top and a flashing green in the middle with nothing underneath or a red could be underneath. the flashing just upgrades the speed. limited is 45 medium is 30 and slow is 15. so the middle aspect is medium and the bottom aspect is slow and the flashing upgrades the speed. so green in the bottom is slow if green flashing in the bottom upgrades it to medium. green in the middle is meduim if it is flashing it is limited. limited clear in plain english means 45 mph through the switch then proceed and say the speed for the track you were coming off of and going onto was 50 then you go 45 through the switch and then after the rear of the train clears the switch you can pick it up to 50 provided you havent passed anotherr signal that restricts the speed of the train. in a nutshell that is it for us anyways i know there are a lot of signals out there just depends on what that subdivision runs on.

later
csx381
 
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