Why are they placed every few miles, what is their function, what do their lights tell? Here's a set of intermediates just on the east side of Tunnel 26 on the old D&RGW:
To keep trains that are moving in the same direction spaced in between sidings. They signals should show Red, Yellow or Green - Green meaning the next two sections are clear, yellow meaning the next section is clear (proceed at restricted speed) and Red meaning - stop, there's a train up ahead.
Is there a standard for how long they light before a train arrives? This info would be good, while hiking along the ROW in mountainous territory...
Signals are fascinating, but don't always tell you when a train is coming. I think it depends on the railroad. Harold
Pretty much to indicate what they are intended for and that is block occupancy. Generally on CTC,and notice I said "generally" the signal aspect would be green, flashing yellow(or double yellow),solid yellow, and red. the indications could be "clear", "approach medium", "approach" and "stop". This is especially helpful on high speed main lines to give the train crew sufficient warning as to track conditions ahead and allow time to properly maintain train control and speed, this could be due to an occupied block ahead or that your train will be entering a diverging route. On the BNSF the double yellow aspect is the one used most often to indicate a diverging route ahead. Most railroads will designate an intermediate signal by a number board or sometimes a letter(ie. "G"). On the BNSF a red aspect on an intermediate signal gives the indication "Stop and Proceed". Which means to bring your train to a complete stop and then proceed at restricted speed until the leading wheels have reached a point where restricted speed is no longer required(ie a more "permissive" signal). Does that help any? CT
Some railroads the signals are lit constantly, others are "approach lit" which means they activate when an approaching train activates the signals preceeding the one you're looking at.
In my opinion, I would think the only thing to watch for is the signal to light up. You are hiking in mountainous territory so you most likely can observe only one signal. By the time you get to the next, quite a bit of time will have passed. If the system is designed to illuminate only when an approaching train enters the circuit or signal block, you will have to start setting up for your shot. The train will likely be moving rather slowly since you are in mountainous territory. If one side of the signal was illuminated red, and the other was anything other than red, I would guess that a train was approaching toward the side of the signal that was not illuminated red. With a signal system that is constantly illuminated, one side of the signal should always be illuminated red if the system is set up for an approaching train. If not, then the system is in a "neutral" setting and no direction has been established in the system. One thing you must always remember: JUST BECAUSE THE SIGNALS ARE DARK DOESN'T MEAN THERE ISN'T ANYTHING ON THE RAILS! TRACK MACHINES OR HIGHRAIL VEHICLES WILL NOT TRIP THE SIGNAL SYSTEM!! EXPECT MOVEMENT IN ANY DIRECTION, ANY TIME!!!!! Another way to learn of the operation of signal systems is to go out someplace where you can see several signals in a row and watch how they illuminate as a train passes through. Especially in the evening hours.
Faor an excellent easy to read essay on railroad signal systems check out Al Krug's website at: http://www.alkrug.vcn.com/rrfacts/signals/signals.htm
