An understanding of distant signals please

[AntonyVW]

Ok I have always assumed that distant signals were to warn that you were entering a given block. Usually placed a short distance (maybe half mile to mile or so) on the approach to a station. I finally got around to buying S&C today (courtesy of the discount ) One of the things I noticed fairly quickly was the use of distant signal in places I could not understand why (particularly with a home signal above it). So my question is - when and where is it appropriate to use distant signals (and also combined distant/home signals)?

 

[NickieFoenshauge]

The distant informs you about the state of the next signal. If the next is red, the distant will be yellow. This should caution you, that you must be prepared to stop at the next signal.

 

[nexusdj]

Distant signal : An advanced warning of the next stop signal or other specified place to which it applies (Amended wording from the current Network rail rule book).

Stop and distant on the same post is used when the distance between 2 signalboxes (block posts) is too short to place a separate distant signal and still be able to stop a train from line speed at its associated stop signal .
The stop arm is worked by the signalbox at that location
The distant arm is worked by the signalbox ahead .
Both are interlinked so that the distant can't be pulled off unless the stop arm is in the off (proceed) position .

 

[AntonyVW]

Thanks both for the information

 

[Mouse84]

NickieFoenshauge and nexusdj are correct. On US roads, usually the distant signal is an automatic signal(block controlled) before an interlocking or control point(dispatcher controlled). The distant signal will indicate how to approach the next signal, prepared to stop, prepared to diverge or whatever. On some roads, such as GCOR ruled, if you are going to get a stop at the CP point, you will get an Advanced Approach at the signal before the distant signal to warn you to be prepared to stop at the second signal. Those are nice if you have a heavy train.

On NS where I run, we have 4 CPs in a row, so the distant to one CP is actually another CP signal.

CP Erwins -------------------------CP GM-------------------------------------------------------CP Corning---------CP Gibson This is 50 mph railroad.

An example Erwins to GM is only 7000 ft. GM to Corning is 2 miles. Corning to Gibson is only 1/4 mile.

Traveling west Gibson towards Erwins, If you have a red at Erwins, Gibson displays clear, Corning displays Approach Medium(30 mph) to get you slowed before the Approach at GM, so you can get stopped at Erwins.
Traveling east Erwins toward Gibson, if you have a red at Gibson, Erwins displays clear, GM displays Approach Slow(15 mph), so you can get it slowed for the Approach at Corning and get stopped for the Red at Gibson.

 

[bwfeldsee]

Nexusdj has given an accurate summary of the priciples though there are, as you might expect, lots of variations on the theme according to location.
A typical scenario is to have a distant (yellow arm) followed by two stop signals (red arms). The first of these is called a home signal and the second a starting signal. Take a small station on a double track line as an example. The distant signal is placed at a suitable braking distance from the home signal which is itself most likely at the entrance to the station. Then at the other end of the station (at the platform end) is the starting signal. For the distant signal to be pulled off, BOTH the home and starter must be at clear so there is no danger of running at full speed into the station and finding the starter at danger.
If the next station down the line is close, the distant signal for that station will be on the same post as the starter at the first station. This often happens on suburban lines where the distance between stations is small and trains run close together.
Yet another variant is to have a fixed distant - one which is ALWAYS at caution and can't be pulled off. This used to be very common on single track branch lines with passing loopps where you would always want the train to enter the station slowly.

Hope this helps.
Alan

 

[teddytoot]

A slight correction to the above. The line is divided into blocks and the first signal is the starter signal which allows entry to the block. The distant gives warning, and stopping distance for the state of the home signal which can normally only be clear if the starter signal for the next block is clear. Modern four aspect colour signals work on a slightly more complicated pattern.

 

[AntonyVW]

Thanks all. I can see that signals are not as complex if they are broken down into small areas.