Signaling | Signal Aspects and Indications

When trains began to use signals, they used them to indicate a particular route like their European counterparts. As the railroads became larger, the signals were used to indicate speeds instead of routes.  In some ways, the speed and the route corresponded.  For one reason or another, as the route changes the allowable speed will also usually change.

SPEED LIMITS

Trains have speed limits depending on the track conditions and the train consists.  Trains do not use speed limit signs like highways.  Trains use signals so that the speed limits can change automatically or can be easily changed by a dispatcher    These speed restrictions listed below come in intervals with maximum limits: 

 

NORMAL SPEED is the maximum authorized speed that the track will allow.  Normally 60 MPH for freight and 70 MPH for Passenger

 

LIMITED SPEED is not exceeding 45 MPH for passenger and not exceeding 40 MPH for freight.

 

MEDIUM SPEED is not exceeding 30 MPH

 

SLOW SPEED is not exceeding 15 MPH

 

RESTRICTED SPEED.  Prepare to stop within one-half the range of vision-short of a train, obstruction or switch improperly lined.  Be on the lookout for a broken rail.  Speed must not exceed 20MPH outside of interlocking limits or 15 MPH within interlocking limits.  This speed applies to the entire movement.

TYPES OF SIGNALS

 

INTERMEDIATE SIGNALS are usually placed on a main line between control points.  Intermediate signals are used to space trains out traveling in the same direction, one behind the other.  Intermediate signal usually have just one target.

 

HOME SIGNALS are usually placed at control points.  These are usually points where the train can take a diverting route or pass another train.  Home signals usually have two or three targets.  This allows home signals to display some aspects that intermediate signals can not display. 

1. SIGNAL ASPECTS | click to download Signal Aspects pdf

To make this easier to understand, I have not attempted to do all possible signal aspects.  I have concentrated on those that will be most useful on your model railroad.  I have also grouped these by the different signal types and common names.

Speed Clear               Speed Approach       Approach Speed         Most Restrictive

2. SIGNAL INDICATIONS THAT CORRESPOND TO THE SIGNAL ASPECTS ABOVE

The signal aspects above are light or position displays that are interpreted by the engineer of the train.  The rule that corresponds to that aspect is called the INDICATION.  I will state the rule from the NORAC rule sheet then I will give my interpretation of the rule for model railroading.  Print out the particular aspect page you will be using on your model railroad and use it with the indication below.

I will group these like the columns above:

SPEED CLEAR aspects

CLEAR.  Proceed, not exceeding Normal Speed

This means that the track is clear for at least 2 signal blocks ahead of the train.  The “normal” speed is maximum the track permits for that particular train consist.

LIMITED CLEAR.  Proceed at Limited Speed until the entire train clears all switches and then proceed at normal speed.  Trains not equipped with cab control, must approach the next signal at Limited Speed.

This would be used where the train is passing through longer and higher speed switches to a clear route.

MEDIUM CLEAR.  Proceed at Medium Speed until the entire train clears all switches and then proceed at normal speed.  Trains not equipped with cab control, must approach the next signal at Medium Speed.

Same as above where the switches are shorter and not high speed switches.

SLOW CLEAR. Proceed at Slow Speed until the entire train clears all switches and then proceed at normal speed.  Trains not equipped with cab control, must approach the next signal at Medium Speed once they have left the interlocking.

This is where the train is passing through a more complicated configuration of switches.  This seems the same as above except the train is allowed to increase speed to Medium Speed, not normal speed, once clear of the interlocking.

All of the above are normally used when the train is LEAVING a slower territory.

SPEED APPROACH aspects

APPROACH.  Proceed prepared to stop at the next signal.  Trains exceeding Medium Speed must begin reduction to Medium Speed as soon as the engine passes the Approach Signal.

This occurs in different situations.  One can be anywhere the next signal is a Stop Signal.  Another is when the train is approaching slower territory where the next signal may not be stop, but a more restricted speed. 

ADVANCED APPROACH.  Proceed prepared to stop at the second signal.  Trains exceeding Limited Speed must begin reduction to Limited Speed once the engine passes the Advanced Approach Signal.

This signal is used in higher speed territory where it may take more time for a train to slow down.  It can also be in higher density territory where trains are following each other more closely.  Notice how the next signal will be approach and the speed is further reduced.  Use the BSF to get the flashing aspect.

MEDIUM APPROACH.  Proceed prepared to stop at the next signal.  Trains exceeding Medium Speed must begin reduction to Medium Speed as soon as the Medium Approach Signal is clearly visible.

This aspect can be used when the train is approaching a switch that will send it on a diverting route.  The diverting route will have another configuration ahead so that the train is not allowed to resume normal speed once clear.  One common use is turning on to a passing siding.  Use the BSF to get the flashing aspect.

SLOW APPROACH.  Proceed prepared to stop at the next signal.  Slow speed applies until the entire train clears the switches, then Medium Speed applies.

Again, the track configuration means slow speed.  These would be passing through slow speed switches, but still going into medium speed territory.

APPROACH SPEED aspects

MEDIUM APPROACH MEDIUM.  Proceed at Medium Speed until the entire train clears all switches then approach the next signal at Medium Speed.

This is similar to Medium Approach, but the train does not have to be prepared to stop at the next signal. 

APPROACH LIMITED.  Proceed approaching the next signal at Limited Speed

This is used well in advance to slow the train down to at least Limited Speed.  The engineer does not expect to have to stop at the next signal.

APPROACH MEDIUM.  Proceed approaching the next signal at Medium speed.

This is used to slow the train down to at least Medium Speed.  It could follow an Approach Limited signal to slow the train down even further.  Again, the engineer is not expecting to have to stop at the next signal.

APPROACH SLOW.  Proceed approaching the next signal at Slow Speed.  Trains exceeding Medium Speed must begin reduction to Medium Speed as soon as the engine passes the Approach Signal.

This is used to slow the train down even further to Slow Speed.  It could follow the Approach Medium Speed to slow the train down to Slow Speed.  Again, the engineer is not expecting to have to stop at the next signal.

MOST RESTRICTIVE aspects

RESTRICTING.  Proceed at restricted Speed until the entire train has:

1. Passed a more favorable signal, or

2. Entered non-signaled DCS Territory, or

3. Passed a location where a more favorable cab signal was received.

This is used where something in the environment or the track condition itself does not permit the train to go any faster than Restricted Speed.  In this case, the engineer must be prepared to stop the train for various conditions. 

 I once saw a train on the Gilford RR that was restricted to 10 MPH for 30 miles because of poor track condition.  The train did not have to stop, just go slowly enough that minimal forces were applied to the track.  You could simulate this on your model to add some interesting operations.

STOP AND PROCEED.  Stop and then proceed at Restricted Speed until the entire train has:

1. Passed a more favorable signal, or

2. Entered a non-signaled DCS Territory, or

3. Passed a location where a more favorable cab signal was received.

Where the letter “G” (grade marker) or the letter “R” (restricting marker) is displayed in addition to number plate (MP Sign) as part of these aspects, freight trains may observe the signals as though Restricting Rule was applied.

This indication is used on most intermediate signals.  Normally it is the mile post sign on the signal that makes it a permissive signal.  As an example, assume a train is traveling on a single track main line with 30 miles between control points.  Half-way to the next control point, one of the intermediate signals is Stop.  Instead of the train waiting for an inspection team, it is allowed to stop and proceed ahead while looking for the reason the signal is Stop.  If the next signal is more favorable, the train can move ahead at that speed. 

STOP.  Train must stop and remain stopped until a more favorable signal aspect appears. 

This is usually called an absolute stop or absolute signal.  These signals are usually home signals located at a control point.  Trains are not allowed to proceed ahead because this is the point where opposing or crossing trains pass each other.

I hope that this helps you to further understand Railroad signals.  A better understanding will lead to more prototypical operation of your model railroad.  This will have you change from a rail fan watching your trains to an engineer watching your signals.   

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