Dark Signals

I was watching the CSX mainline yesterday around 12:30 at the north end of the Howard St. tunnel and I saw something weird.

When I got there, the aspect signal guarding the tunnel was off. No lights at all.

I sat there for about 20 minutes, and suddenly the smell of disel got stronger and stronger and then I heard a noise so I walked down and waited. The train came out of the tunnel and the signal turned red.

I dont understand this. Why was the signal (which would only be seen by southband traffic, off while the train was in the tunnel? Shoudln't the signal be red while the train is in the tunnel and then go off or turn green when the tunnel is empty. I think a southbound train woudln't even see the red signal because of the large train coming out of the tunnel.

To save light bulb life, and electricity, lot's of signals are "approach lit". This means they remain dark, until a train is in "the circuit", and the signal would need to be seen, for a reason. It could be red, yellow or green, when lighted, depending on what's in store, for the movement in question. A fairly good tool to use, when looking for trains. No signal, no train, so to speak..........
When that train passed the signal, it "entered the block" and therefore, the circuit was complete, and the signal displayed. It doesn't matter what direction the traffic is moving. Block occupancy is block occupancy, and a train in a block, needs a signal. (in signaled territory) That signal probably remained lit, until the train cleared the block, and then, being no longer needed, turned off, again. Regards

So perhaps there is a second signal inside the tunnel that he would have seen?

You are too fixated on that tunnel. The signals are there for the track blocks, not the tunnels, or bridges. a VERY average track block length is APPROXIMATELY 2 miles. go that distance, in either direction, and look for the next signal. There is nothing special, about the tunnel, except you might stay dry inside of it, while it's raining . As a matter of fact, a signal in a tunnel would be an operating headache. How would you fit it into the tunnel, most of which are just large enough to clear a train through them. Tunnels cost money, and it is not built any larger than needed. Next, who is going to go inside the tunnel, to test, inspect and service that signal? Operationaly speaking, the signal is easier to mount outside the tunnel, rather than in it. (that's where you saw yours, right?)
Signals, in most cases, indicate track occupancy, not "tunnel status". Unless a train is in the tunnel, there is no need to relay tunnel info, to a train. Not to be confused, with a slide fence/falling rock signal, but that's not what you indicated you saw. Regards

Again, if the tracks were single tracked through the tunnel, it is not an issue. Those signals are protecting the block, between opposing signals. It doesnt matter that it's through a tunnel. The signals protect/convey info, regarding the block, not the tunnel. By definition, if it's an "Interlocking", that's the only way those switches and signals, can work. The tunnel is irrelevent.

GOLDEN-ARM wrote:It doesn't matter what direction the traffic is moving. Block occupancy is block occupancy, and a train in a block, needs a signal. (in signaled territory) That signal probably remained lit, until the train cleared the block, and then, being no longer needed, turned off, again. Regards

This statement is correct if its ABS that is used. If APB is the system/logic deployed then direction of the train does make a difference, not for a single signal guaring a block, but for a whole slew of signals guarding miles of bi-directional track.

gprimr1 wrote:I was watching the CSX mainline yesterday around 12:30 at the north end of the Howard St. tunnel and I saw something weird.

When I got there, the aspect signal guarding the tunnel was off. No lights at all.

I sat there for about 20 minutes, and suddenly the smell of disel got stronger and stronger and then I heard a noise so I walked down and waited. The train came out of the tunnel and the signal turned red.

I dont understand this. Why was the signal (which would only be seen by southband traffic, off while the train was in the tunnel? Shoudln't the signal be red while the train is in the tunnel and then go off or turn green when the tunnel is empty. I think a southbound train woudln't even see the red signal because of the large train coming out of the tunnel.

Am I missing something here? I read your text over and over and I come to the conclusion that the signal 'face' can be seen upon approaching the tunnel. If this is the case then I believe you are correct, this signal should have been lit red because the block behind it (which at least a portion of it is in the tunnel) is occupied. Regardless if it is ABS or APB logic the signal should have been lit red.

If howver the signal is pointing the other way, that a train leaving the tunnel would see its 'face', then its aspect could have been any color since its guarding the block ahead of the train.

What has caught my attention is that you said it lit up after it was passed and this is not the usual behavior for an approach-lit signal. Usually it is dark, then turns green once a train gets within a few blocks of it. Then when passed it goes from green to red. As the train moves down the track it will go from red to yellow, and eventually yellow to green. The amount of green time before it goes dark varies with the railroad. I know of signals that go yellow to dark (no green time) if there are no more trains coming.

A signal, in "approach lit" territory, will remain dark, even with a train sitting dirctly behind the rear of the signal. Until a train occupies the block, in the block with the face of the signal, it will remain dark. If he saw the signal turn red, after the train entered the block, being occupied by his engine, the block occupied by his train would be a red block. This is what he saw. If you have ever travelled at higher speeds, you may notice, that as you pass the rear of a signal, and turn around to see it's face, it will remain dark, for several seconds, until it lights up, red. The blocks are protected for traffic entering the block, not leaving it. If there is no traffic entering a block, there is no need to display a restrictive signal for that block. YOU become the reason the block is occupied, as your train occupies it, no matter the direction. You have already lit the approach into the block, by occupying the previous block. A block, although governed by the next block adjacent to it, in either direction, does not necessarily light a signal, until the approach to that particular block, is occupied. I have also seen, in tangent territory, the blocks go dark, as I cleared them, from the following block. The same applies to blocks ahead. If you have travelled in long stretches of tangent territory, at night, you can see the signals "come to life", as you occupy the approach block, to that signal. (not an approach signal) You can see the clears light up, as you hit each block, and are advancing on the next. They also extinguish, in the same order. As you clear the occupancy of each block, the signal protecting following movements goes dark, until the next time the block is occupied, hence a reason to convey that info. This doesn't apply to Interlockings, some switch indication lights, etc. With the advent of LED bulbs, it seems almost like a waste, to maintain the extra electronics, for an approach lit system, with the long bulb life, and low electricity useage, of LED's. Just a thought.........

GOLDEN-ARM wrote:With the advent of LED bulbs, it seems almost like a waste, to maintain the extra electronics, for an approach lit system, with the long bulb life, and low electricity useage, of LED's. Just a thought.........

I agree, but from a rail fanning perspective I hope this doesn't happen. Approach-lit is a good way to confirm to a rail fan that a train is about to go by. If its on all the time it could be hours before a train goes by. I've gone to a good spot to watch a train and the signal is dark.....5 minutes later it lights green....and I know the train is on schedule.....10 minutes later.....shoowsh....she goes by!

GOLDEN-ARM wrote:A signal, in "approach lit" territory, will remain dark, even with a train sitting dirctly behind the rear of the signal. Until a train occupies the block, in the block with the face of the signal, it will remain dark.

In my mind that is a serious flaw in an ABS/APB implementation. The block is occupied and the signal should be red.....its as simple as that. From what I can gather it seems this type of implementation occurs only in the US....my observations in Canada see signal lighting well before a train gets near them.

Why SHOULD it be red? If there is no train approaching that signal, why convey information? It sounds like you want it to be more "railfan friendly", so you will know when a train is approaching............ Probably not a consideration, when the C&S people, are designing the system. I can think of no plausible reason, for lighting signals, in approach lit territory, other than for trains occupying blocks, can you?

GOLDEN-ARM wrote:Why SHOULD it be red? If there is no train approaching that signal, why convey information? It sounds like you want it to be more "railfan friendly", so you will know when a train is approaching............ Probably not a consideration, when the C&S people, are designing the system. I can think of no plausible reason, for lighting signals, in approach lit territory, other than for trains occupying blocks, can you?

(1) Suppose there is a fault in the circuitry in the block immediatly before the occupied block??? By having approach lit circuitry in a few blocks before the occupied block, you have multiple opportunities to light the signal before a train approaches it. This is a failsafe fundamental.

(2) A train engineer has more time to observe and react to a signal that is visually confirmed at a distance versus waiting till the last minute to get its color. There is a big difference between having a signal light red or green at the last minute versus being seen red or green half a mile away. I'm coming down the track at 60MPH/100KPH expecting it to approach light green and it actually lights red.....what do I do other than brake hard?

I couldn't care less about signals being rail fan friendly....I like it when they are, but I couldn't care less.

The signal faces north so that only southbound trains can see it.

http://www.gregsphotos.info/howard.jpg

I took that last time for anyone who wants to see what I"m trying to describe.

My thinking was that if a train ended up at the tunnel mouth because of a signal failure or something, and saw the final red before going in the tunnel, it could throw the switch in front of the tunnel and put the norhtbound train on the second track until CSX could sort it out.

I'm having a hard time following some of the logic here.
As G-A pointed out, the signal is approach lit. It lights when there's someone to see it; occupancy of the next block does not necessarily have a bearing on whether the signal is lit or not.
As far as having a signal coming on at "the last minute" - don't you think the people who designed the system take the amount of time it takes to stop a train into account? Again, like G-A stated - blocks are plenty long, and the signals come on in plenty of time.
In the case of a failure of some sort, there are provisions for that too. Any signal that is "improper" is regarded as having the most restrictive indication that signal can display.
Chris

My thinking was that if a train ended up at the tunnel mouth because of a signal failure or something, and saw the final red before going in the tunnel, it could throw the switch in front of the tunnel and put the norhtbound train on the second track until CSX could sort it out.

Sorry, but this makes no sense. Main line railroading just doesn't work this way.