RAILforum: Why Use Semaphores?

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Posted by Konstantin (Member # 18) on :

I recently rode the Southwest Chief. I noticed that a little east of Albuquerque, there are semaphores instead of regular light signals. This is an area where the Southwest Chief is not on the regular Santa Fe mainline (actually BNSF now).

Why do they use semaphores? I am guessing that since this is a little used area of the railroad, that they just have not bothered to replace them with lights yet. But, I still wonder why they were used to begin with. It seems that lights are much simpler and would require less maintenance. So why did they ever use semaphores instead of lights?

Thank you

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Elias Valley Railroad (N-scale)
www.geocities.com/evrr

Posted by MPALMER (Member # 125) on :

At the time the semaphores were installed, mechanical technology was the affordable and more reliable way to go. The semaphores had to work reliably through all types of weather and in a wide range of temperatures.

Posted by Eric (Member # 674) on :

Believe it or not, but many locomotive engineers prefer semaphores over lights. In bad weather, such as snow, where visibility is low, the crews have a better chance of seeing a semaphore arm than a light, because the light may be covered up by the snow.
It is also easy to spot at far distances, because the arm is vertical on a clear, and horizontal on a stop indication.

Posted by Charlie McCandless (Member # 939) on :

Living in Raton for three years spoiled me on semaphores. They are a lot easier for a railfan to see in the daytime. This is good especially for one without a scanner. I am sorry to see them go.

PS The railroad musueum in Pueblo has some. Hopefully we will put them up soon.

Posted by Kent Loudon (Member # 902) on :

Actually, I wonder why it is currently necessary to have trackside signals at all.
With modern technology, couldn't track conditions or occupancy be transmitted directly to locomotive cabs on a continuous basis, with radio communication for backup?

Many railroads, notably Pennsy, had "cab signals" fifty years ago!

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- Kent Loudon, Somerville NJ

Posted by Konstantin (Member # 18) on :

Thank you for your responses.

Kent, I was wondering the same thing. Why signals at all. With GPS navigation, it seems that they would know exactly where every train is all of the time.

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Elias Valley Railroad (N-scale)
www.geocities.com/evrr

Posted by MPALMER (Member # 125) on :

GPS was discussed in a rail magazine a few years ago. Some railroads are looking in to using it. At that time, GPS was accurate, but not THAT accurate. It could locate a train, but it could not tell if it was on the main track or an adjacent siding.

GPS locators need to be able to lock on to two or more satellites to verify location. This would not be possible in some confined areas (tunnels, steep valleys, etc.)

Do you know if GPS can now work in these areas?

Posted by barrydraper (Member # 737) on :

First, Semaphores are left overs from pre-1920 signal installations that the railroad has not yet justified the money to replace. The reason for semaphores from the beginings of signalling around 1870 until the 1920s is that electric lights were not bright and reliable enough. Semaphores originally used oil lamps for the night indication. These were replaced by dim electric lamps when these became available.
There are in fact places (mostly in the East, but also the C&NW across Iowa) where cab signals are used and no lineside signals are installed, but these don't use GPS technology. Remember, signals are a safety device, so they MUST be designed to fail-safe, that is ANY failure must not result in a train getting clearence to be where it is not susposed to be. GPS and other computers just aren't quite up to that level of reliabilty yet, but tests are still being carried out.

Barry Draper

Posted by The Safety Valve (Member # 971) on :

Eric writes...

<...many locomotive engineers prefer semaphores over lights. In bad weather, such as snow, where visibility is low, the crews have a better chance of seeing a semaphore arm than a light, because the light may be covered up by the snow.>

I'm a 30-year engineer, Eric, and I never heard anyone say they preferred the arms over the lights. There are a hundred reasons why semaphores are harder to view at a distance than colour lights. Can't imagine where you heard this!

Also, I never heard of a signal being covered by snow! Colour light signals have a hood above the lens which would obviate this - not to mention the fact that the heat generated by the unit would--I imagine--ensure that snow couldn't cover it - not to mention the fact that it would be a helluva deep snow drift that would cover a signal post!

Re use of GPS:
Here in the state of New South Wales in Australia, the track owner--Rail Infrastructure Corporation--have some train order areas that utilise GPS to confirm the location of the train (read 'locomotive'). Train orders and any reporting points written thereon are given codes (alpha-numeric, randomly-generated by the dispatcher's computer) which are quoted back by the engineman (usually the co-driver) over the radio or sat-phone to the dispatcher as required by the train order. When the dispatcher enters these codes into their workstation, the system ensures the dispatcher cannot give a train order in conflict with any other. GPS ensures that the train is where the engine crew are saying it is, otherwise the systen alerts the dispatcher.

Regards,
The 'Valve

Posted by Gil Abar (Member # 990) on :

quote:
Originally posted by The Safety Valve:
Eric writes...
Also, I never heard of a signal being covered by snow! Colour light signals have a hood above the lens which would obviate this - not to mention the fact that the heat generated by the unit would--I imagine--ensure that snow couldn't cover it - not to mention the fact that it would be a helluva deep snow drift that would cover a signal post!
Regards,
The 'Valve

You will find that some of the blizzards with high winds in the US will cover the signal lense with snow. There is no heat from the signal buld as it is a 10 volt 25 watt and the small amount of heat is rapidly disapated in below freezing conditions. Some of the newer color light signals use LEDs in place of bulbs. The State Rail of NSW was testing this type signal in 1993 while I was there.

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SignalGil

Posted by Charlie McCandless (Member # 939) on :

Talk of GPS reminded me of one engineer's lament. While talking about GPS and internet tracing of equipment he said ``They still can't tell me with any certainty when I am going to go to work.''

Posted by Eric (Member # 674) on :

The Safety Valve,
I heard about the semaphores from a railroad video. The engineers were discussing semaphores and said that they, and others, would rather have semaphores than lights.
In states such as Colorado, New Mexico, Arizona and a few others, very heavy, sideways snow often falls and creates poor visibility. The engineers talked about having to slow down or stop trains to see what the indication was.
Do locomotive crews run by cab signaling when they reach a dark signal, or do they have to stop when the indication isn't visible?

Posted by Charlie McCandless (Member # 939) on :

Eric,

A dark signal is considered red. Trains must stop and recieve permission from the dispatcher before proceeding. One burnt-out light bulb can cause a lot of havoc on a heavily trafficed line. An article on signals appeared in the July issue of TRAINS Magazine.
Incidentally, the signals on the Santa Fe's Northern line are linked to Automatic Train Stop. When the Federal Government regulated speed limits on trains in 1947 automatic Train Stop was required on all lines where trains operated at 80 mph or faster. (This is why railroads have that weird 79-mph speed limit on signalled territory that doesn't have ATS.)
If the signal is other than green, a plate next to the signal is energized. It may be physically moved, I don't know. The engineer has to acknowledge that signal by pressing a button when a show on the locomotive passes over the plate. If he or she doesn't the train is stopped automatically.
There are some permanently mounted plates on Raton Pass where the engineer always has to press a button.
On places where there aren't signals (dark territory) freight trains are limited to 49 mph, passenger trains, 59 mph.

Posted by Gil Abar (Member # 990) on :

Charlie - On the old ATSF the ATS is only required on passenger trains and freights run non-equipped.

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SignalGil

Posted by Charlie McCandless (Member # 939) on :

Gil,

You are right. Only passenger trains had ATS because they were the only trains that ran 80 mph or faster. The freight engines were geared for about 70 mph (62-15 gear ratio. I believe the Super-C used passenger-geared engines but speed waslimited to 79 mph by the presence of the caboose. Having ridden cabooses at 60 mph, I can imagine what 79 would fell like.

Charlie M.

Posted by Gil Abar (Member # 990) on :

Charlie - The speed of any train operated in territory equipped with ATS did not matter. Part 236.566 requires that "each" train operated in ATS territory "shall" be equipped with apparatus responsive to the equipment. The ATSF was granted relief to run freight trains "non equipped" by the former ICC. The only trains that are equipped today are Amtrak.

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SignalGil