I'm glad I got to see them last year on our September trip on the SWC, before they were replaced.
Last call for the BNSF Glorieta & NMRX Semaphores
- Thread starter SWRailroadPhotography
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As a signalist, I have a lot of nostalgia for many types of US signals:
Each of these types of signals have advantages and disadvantages, both for the railroad and train crews, and for us railfans.
Searchlights are a master-class on precision optics design. They can be focused so well that they can be seen for miles, and even have to have a little diffraction lens in them to shine a little light down to be seen up close. Their two main disadvantages are that they can only show up to 3 colors, and their moving parts are more-prone to failure. PTC has killed the searchlight, because the searchlight mechanisms themselves form part of the signal circuits—you can't just simply take out searchlights and replace them without re-doing all of it (or spending extra money to patch such a drastic change).
Semaphores are iconic classics because they're simple and easy to read, don't require lights, and their aspect can even be observed from both front and back. They have numerous disadvantages, though: the same moving parts problems as searchlights, the same mechanism-part-of-the-circuit thing as searchlights, and parts for them are long-discontinued and hard to find. In addition, searchlights can only show 2 or 3 aspects at most, and things like flashing aspects are not practical on them without an auxiliary light. Their tall stature and basic ladders aren't the safest either, in modern analysis.
Position Light signals aimed to take the position advantage of semaphores and remove the moving parts. The PRR did a great job of developing and evolving a type of signal that has many lamps to use as little power as possible while still being safe and observable when a lamp is out. A primary disadvantage of Position Light signals are that they're huge (4ʹ4ʺ across or 1.32m) and so must be very tall when positioned between tracks. They also have to be pretty sturdy structures for the wind load on those large targets. They use many lights, though modern LED technology negates this problem. The biggest disadvantage is they aren't capable of displaying all the aspects a modern American speed signaling system needs to employ. Aspects like Slow Clear and Limited Approach and Medium Approach just can't be shown on the high signals.
Color-Position Light signals are the pinnacle of speed signal design, incorporating many unique features and flexibility. Their three biggest strengths are: 1. they only show Red when a stop is actually required [Europeans will greatly appreciate this], 2. all Speed signaling aspects are available, with several safe-failure design features, and 3. the dwarf signals can show all the same aspects as the high signals, and in an identical way. CPLs also maintain the PL advantage of single lamp failure still allowing the intended aspect to be observable. Disadvantages include large structures that are not as massive as Position Lights but can be tall and heavy, many lamps (7+) to maintain on each signal, the unique marker light system which must be memorized, the width-space a complex signal can take up, and potential for confusion of adjacent signals' marker lamps.
No matter what happens on the mainlines, it's reassuring to know that these types of signals all have places in museums so they will not be forgotten.
Each of these types of signals have advantages and disadvantages, both for the railroad and train crews, and for us railfans.
Searchlights are a master-class on precision optics design. They can be focused so well that they can be seen for miles, and even have to have a little diffraction lens in them to shine a little light down to be seen up close. Their two main disadvantages are that they can only show up to 3 colors, and their moving parts are more-prone to failure. PTC has killed the searchlight, because the searchlight mechanisms themselves form part of the signal circuits—you can't just simply take out searchlights and replace them without re-doing all of it (or spending extra money to patch such a drastic change).
Semaphores are iconic classics because they're simple and easy to read, don't require lights, and their aspect can even be observed from both front and back. They have numerous disadvantages, though: the same moving parts problems as searchlights, the same mechanism-part-of-the-circuit thing as searchlights, and parts for them are long-discontinued and hard to find. In addition, searchlights can only show 2 or 3 aspects at most, and things like flashing aspects are not practical on them without an auxiliary light. Their tall stature and basic ladders aren't the safest either, in modern analysis.
Position Light signals aimed to take the position advantage of semaphores and remove the moving parts. The PRR did a great job of developing and evolving a type of signal that has many lamps to use as little power as possible while still being safe and observable when a lamp is out. A primary disadvantage of Position Light signals are that they're huge (4ʹ4ʺ across or 1.32m) and so must be very tall when positioned between tracks. They also have to be pretty sturdy structures for the wind load on those large targets. They use many lights, though modern LED technology negates this problem. The biggest disadvantage is they aren't capable of displaying all the aspects a modern American speed signaling system needs to employ. Aspects like Slow Clear and Limited Approach and Medium Approach just can't be shown on the high signals.
Color-Position Light signals are the pinnacle of speed signal design, incorporating many unique features and flexibility. Their three biggest strengths are: 1. they only show Red when a stop is actually required [Europeans will greatly appreciate this], 2. all Speed signaling aspects are available, with several safe-failure design features, and 3. the dwarf signals can show all the same aspects as the high signals, and in an identical way. CPLs also maintain the PL advantage of single lamp failure still allowing the intended aspect to be observable. Disadvantages include large structures that are not as massive as Position Lights but can be tall and heavy, many lamps (7+) to maintain on each signal, the unique marker light system which must be memorized, the width-space a complex signal can take up, and potential for confusion of adjacent signals' marker lamps.
No matter what happens on the mainlines, it's reassuring to know that these types of signals all have places in museums so they will not be forgotten.
