Signal reading tips

Converting a 1 or 2 headed signal into a 3 headed signal by adding an imaginary red might help you to interpret the signal.

Mast signals:

• If there is only one head on the signal, then add 2 imaginary reds on the bottom.
• If there are only 2 heads on the signal, then an imaginary red is added as follows:
  • If the upper signal is red, then add an imaginary red on top.
  • If the lower signal is red, then add an imaginary red on the bottom.
  • If neither of the signals is red, then add an imaginary red on the bottom.
  • Rule 410 is an exception. Where

    Yellow

    /

    Red

    becomes

    Yellow

    /

    Red

    /

    Red

    .

2 Headed Low-Mast signals (formerly known as Dwarf signals):

• If the upper signal is yellow and the lower signal is green, then add an imaginary red on the bottom.
• If both signals are yellow, then add an imaginary red on the bottom.
• For all other combinations add an imaginary red on top.

Single Headed Low-Mast signals:

• Always add 2 imaginary reds on top.

1. If the signal is not all RED it is not red at all. All red = stop.

2. If you have only 1 LIGHT with colour and it's YELLOW, the name will end with the words '...TO STOP'.

3. If you have only 1 LIGHT with colour and it's GREEN, the name will end with the words '...TO CLEAR'.

4. If you have a SOLID YELLOW ON TOP, the name will start with the words 'CLEAR TO...'.

4a. If you have a SOLID YELLOW ON THE BOTTOM and NO OTHER COLOURS, then it's RESTRICTING.

5. When a signal has 2 lights with colour and the colour is not in the top position (ex: top is red). Then the following modifier applies when naming the colours:
   flashing green = Limited
   solid green = Medium
   yellow (solid or flashing) = Slow

*Exceptions*
On a Double LowMast signal:
   2 YELLOW lights is 'CLEAR TO SLOW'.
   2 GREEN lights is 'CLEAR'.

Hint:
  When naming the colours always start with the colour in the highest position on the signal and finish with the name of the lowest colour.
  The highest colour tells you what to do at the signal (ex: 'clear to...') and the lowest colour tells you how to approach the next signal (ex: '...stop').

** Signal Modifiers **

Letter Plates:
   A: Either slow or stop, depending on signal.
   DV: Diverging.
   L: Limited.
   R: Restricting. Adding R to a 'stop & proceed' changes it to 'proceed at RESTRICTED speed'.

Flashing:
  A flashing light will make a signal more permissive. A 'Medium to Clear' signal with a flashing green, becomes a 'Limited to Clear'.

  Please keep in mind that even though a signal may be logically interepreted to mean something doesn't mean that it's the correct interpretation.
   For example:
      Green
      Red
      Green
      Is rule 407 - Clear to Medium.
  Now, consider what happens when there is a L plate attached to the mast. The L plate should modify the signal to mean clear to limited. However as per the rules clear to limited will never be displayed like that. The ruling is correct but the correct interpretation of that signal is clear to medium.
  Thanks to Jesse D for pointing this out and providing a great example.

** Mast Signal Position **

TOP: Governs HIGH speed route.
MIDDLE: Governs MEDIUM speed route.
BOTTOM: Governs SLOW speed route.