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tri-light signals
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manheim_rails
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tri-light signals
 
« on: Sep 9th, 2011, 3:30pm »
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For the time being I will be spending alot of time on the NS Mon Line. I was doing some research but I just cant find what Im looking for. There is a signal on the Mon Line down the street from my house and it is what I believe is a tri-light signal. It is 3 lights in a upside down triangle. Then there is a signal below it which has just 2 lights. If its a single track line, what is the purpose of the lower signal? Why does it need 2 for one direction? By the way its only for southbounds. The northbound signal has just one.
 
For example earlier today I saw the top signal was yellow and the bottom signal green. (Most of the time the bottom is red) What would this mean? Any information is greatly apprieciated. Thank you.


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k5sss
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Re: tri-light signals
 
« Reply #1 on: Nov 6th, 2011, 11:45am »
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There are two main classifications of US signal aspects: route and speed.
 
Route signals (usually used by Western RRs) indicate which way the train will go at an interlocking; it is up to the engineer to know (from the timetable) the speed limit of the route indicated.  Multi-head signals are required at interlockings but can be found on single-track lines as well.
 
Speed signals (usually used by Eastern RRs) indicate the speed limit of the route ahead.  They do not indicate the route to be taken at an interlocking, but the engineer can often deduce that from the speed and knowledge of possible/likely routes.
 
NS uses speed signals.  A yellow-over-green aspect indicates "Approach Medium", which means a Medium-speed route is available for at least two blocks.  That is likely to be found in advance of an interlocking with a Medium-speed route selected but theoretically could appear anywhere.


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photoman475
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Re: tri-light signals
 
« Reply #2 on: Dec 12th, 2011, 8:47pm »
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The upside down triangle you describe was known at one time as a Type G on some railroads.  There's none around here in the Fargo-Moorhead area on a railroad, but the Fargo school district has installed a few for protecting kids at street crossings!

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