Signalling - Part 2 Flashcards
How does track circuit block system work?
Each section (or block) is connected to the signal in rear via a low voltage current.
Any interruption to the current flow (ie, train wheels) will cause the signal protecting the section to revert to danger
Any other interruption to the track (broken rail etc) will revert the signal back to danger
The track circuit system is designed to be FAIL SAFE
What are insulated block joints?
They are insulated block joints which electronically isolate each signal section from another
What is signal overlap?
Designed as a safety precaution.
A buffer zone after the signal to ensure the train has left the block before the next train is allowed in
What is the distance of a signal overlap?
4 aspect signal - 200 yards
3 aspect signal - 300 yards
2 aspect signal - 440 yards
What is the distance of a signal overlap when there is a 4 aspect signal?
200 yards
What is the distance of a signal overlap when there is a 3 aspect signal?
300 yards
What is the distance of a signal overlap when there is a 2 aspect signal?
440 yards
Where does the most restrictive aspect appear on a signal?
At the bottom
How many aspects can a track signal block signal have?
2, 3 or 4
What does a double yellow aspect mean?
Preliminary caution
Be prepared to find the next signal at caution
(Slow down!)
What does a yellow aspect mean?
Caution
Be prepared to stop at the next signal
(Slow the fuck down!)
After the train passes a green signal what will happen to it?
What about the signal before it?
And the one before that?
And the one before that?
It will turn red
The one before will turn from red to yellow
The one before that will turn from yellow to a double yellow
The one before that will turn from double yellow to green
What do two aspect signals consist of?
STOP and DISTANT signals
Describe a 2 aspect STOP signal?
Green at the top and red at the bottom
Describe a 2 aspect DISTANT signal
Green at the top and yellow at the bottom
It is similar to the colour light signals used in absolute block areas
What does a white triangle on a black background mean on a 2 aspect signal?
Distant signal
What does the R signal mean on a 2 aspect signal?
(Repeater)
Distant signal
Where does the section run from and to on a 2 aspect signal?
From a STOP to a STOP (with a DISTANT signal in between)
What does a white plate with a black HORIZONTAL line mean (on a signal ID plate)?
The signal is automatically controlled (by the passage of trains)
What is a black plate with an ID number in white on it mean?
The signal is controlled by a signaller/physical person
What does a white plate with a black HORIZONTAL line and the word SEMI written on it mean?
Semi-automatic signal - operated either by the passage of trains OR by a signaller
What are distant signals operated by?
Either a signal box, a ground frame or passage of trains. (semi automatic)
Identified by a triangle or a letter R.
