Colour Light Signalling Flashcards
What is the purpose of fixed signals in railway systems?
Fixed signals divide the track into sections to ensure that only one train is permitted to enter one section at one time.
What is 2 aspect signalling?
2 aspect signalling allows only 2 aspects to be displayed in each signal, similar to the semaphore arms they replace.
What aspects can be displayed in 2 aspect signalling?
Distant signals can display yellow or green, while stop signals can display red or green.
What is a block section in 2 aspect signalling?
The block section is the distance between two stop signals.
What is 3 aspect signalling?
3 aspect signalling allows for greater control over train movements by displaying green, yellow, or red aspects.
What is a block section in 3 aspect signalling?
The block section is the distance between two signals on a 3 aspect system.
What are the normal signalling rules for 3 aspect signalling?
A stop signal must have a yellow signal before it. If a signal shows a green aspect, the next signal must also show a proceed aspect (green or yellow).
What are 4 aspect signals used for?
4 aspect signals are used on higher speed lines or where the sections between signals are short to give advanced warning of stop signals ahead.
What additional signal does a 4 aspect signalling system display?
A 4 aspect signalling system can display a double yellow used as a preliminary caution that the next signal is yellow.
What is the future of signals?
The future of signals is LED.
How can a 4 aspect signal be condensed?
A 4 aspect signal can be condensed into 2 aspects, with the bottom aspect being green, red, or yellow and the top one displaying another yellow for preliminary caution.
What are the three main categories of controlling colour light signals?
The three main categories are: 1. Controlled - Operated manually by the signaller or set by the signaller to work automatically. 2. Automatic - Controlled by the passage of trains through a section. 3. Semi-automatic - Controlled automatically by the passage of trains but can be controlled manually from a signal box or ground frame.
What happens when the track circuit is unoccupied?
The current from the power source travels around the circuit, passing through the signal relay, which keeps the green proceed aspect signal light open.
What occurs when a train occupies the section of the track circuit?
The electrical current is short circuited across to the other rail due to the electricity taking the path of least resistance.
Why does the electrical current stop passing through the signal relay when a train is present?
There is less resistance to pass through the train wheels than through the signal relay.
What happens when the electrical current stops passing through the signal relay?
The magnetic field holding the switch open ceases, causing the switch to close and the red stop signal aspect to be displayed.
What are axle counters used for?
Axle counters are used to count the number of train wheels that enter a section.
Where are axle counters fitted?
Axle counters are fitted near the railhead.
What mechanisms do axle counters use?
Axle counters use mechanical treadle or magnetic switch.
When will the signal show a proceed aspect?
The signal will show a proceed aspect only when the same number of train wheels are recorded by axle counters at both ends of the section.
What happens when a train occupies the section between signals?
The signal behind automatically displays a red aspect.
What occurs as the train passes into the next section?
The signal behind the train changes to red and a yellow aspect is shown on the previous signal.
What does the overlap do regarding signal aspects?
It keeps the same signal showing red, creating a safety gap of a whole signal section behind the train.
What happens once the front of the train clears the overlap?
The signal immediately behind changes to red, with the previous signal still showing a red aspect.
When does the previous signal change to yellow?
Only when the whole train has cleared the overlap will the previous signal change to yellow, with the signal behind the train showing a red.
What is permissive working with colour lights?
Permissive working can be controlled by position lights on the main aspect, which can override the main aspect.
What does it mean if the position light (PL) is off?
If the PL is off, this authorises you to proceed past the signal at caution and be prepared to stop at the next necessary point or signal.
Where can position lights be mounted?
Position lights can either be elevated on posts/gantries or mounted on small posts at track level.
What does a stop position on a position light display?
When the PL is in the stop position, it displays two reds or a red and white light horizontally.
What must be done when a position light is in the stop position?
The movement must stop and not pass the PL.
What does it mean when a position light is off?
When a PL is off, it displays 2 white lights at 45°, authorising the driver to proceed with caution.
What should a driver be prepared for when proceeding with caution?
The driver should be prepared to stop short of any obstruction, buffer stop, train, or signal showing a stop indication.
What does a yellow aspect on a position light indicate?
If a position light displays a yellow aspect, it works the same as the yellow shunt discs.
When can movements pass a position light in the on position?
Movements must only pass the PL in the on position if the movement is being made toward the shunt neck and not the running line.
What are junction indicators used for?
Junction indicators show that a train is being signalled to a route to the left or right of the straight route.
Where is a junction indicator typically located?
A junction indicator is normally located above the signal.
What do junction indicators display when a proceed aspect is shown?
They display a line of white lights.
When is a junction indicator not provided?
There is normally no junction indicator provided when the straight route is obvious.
When is a junction indicator provided?
A junction indicator is provided where there is no obvious straight route for all signed routes.
What happens if the straight route is not the highest-speed route?
The junction indicator will normally apply to the lower-speed route.
What is indicated when diverging routes ahead are of equal speed?
A junction indicator will be provided for each route.
What was the previous method for routes set with a reduction in speed?
You used to be checked down to a stop signal before being allowed to pass onto the junction.
What is a limitation of the previous method?
It can cause unnecessary delays on higher speed or more intensively used lines.
How can you be warned of a diverging route ahead?
By showing a flashing yellow aspect prior to the junction signal.
What is the sequence of flashing yellows in 4 aspect signalling?
You can have two flashing yellows before one flashing yellow followed by a steady state yellow with the route set.
What are the three risks associated with this type of signalling?
- You may forget that the single yellow also means a red ahead.
- You may think the previous light was a flashing yellow but it was a steady yellow, so the next signal is red.
- You may be being wrong routed and not realise.
What is a route indicator?
A route indicator is provided at the signal to display either a letter or number indicating the route onto which the movement is being signalled.
What is a preliminary route indicator?
A preliminary route indicator is provided to give advance information about the route set beyond a junction signal ahead.
What is double blocking a junction?
Double blocking a junction involves holding an approaching train 2 sections from a movement that causes conflict, leaving a block section empty in case the driver spads.
What is a route indicator?
A route indicator is provided at the signal to display either a letter or number indicating the route onto which the movement is being signalled.
What is a preliminary route indicator?
A preliminary route indicator is provided to give advance information about the route set beyond a junction signal ahead.
What is double blocking a junction?
Double blocking a junction involves holding an approaching train 2 sections from a movement that causes conflict, leaving a block section empty in case the driver spads.
What is a point indicator?
A point indicator is associated with points and is identified by a sign showing the words ‘Points Indicator.’
What does a red or no light on a point indicator mean?
It means to stop at the points indicator and contact the signaller unless otherwise authorised.
What does a steady yellow light on a point indicator indicate?
It means the points are fitting correctly.
What are banner repeating signals used for?
They are provided to give advanced signalling when a signal is obscured by curvature of the line, a tunnel, building, etc.
What does a horizontal banner repeater signal indicate?
It indicates that the signal it is referring to is at danger.
What does a 45° banner repeater signal indicate?
It indicates that the signal to which it is connected will be displaying a proceed aspect.
What does BR mean on a signal plate?
BR means Banner Repeater.
What does a 3 state BR provide?
It provides additional information to a driver about the signal connected.
What does a green background with a black bar at 45° on a 3 state BR mean?
It means the signal connected to the repeater is green.
What does a white background with a 45° angle on a 3 state BR indicate?
It means the signal will be showing a cautionary aspect either yellow or double yellow.
What does a white background with a horizontal line on a 3 state BR indicate?
It means the signal connected will be displaying a red aspect.
Why is a 3 state BR better?
It is better at identifying what a signal will be.
What are Co-Acting signals?
Co-Acting signals are placed at locations where the main signal cannot be seen or could be easily misread. They repeat what is displayed on the main signal.
CA on a signal plate stands for Co-Acting.
What should you be aware of when stopped at a home signal replaced as a colour light signal?
If you have stopped or nearly stopped, you must be aware that if it turns to green, the next signal may still be red.
What should you remember when entering a semaphore section with a distant replaced by a colour light signal?
If the distant displays caution, you must expect the other signals to be at danger even if the one ahead is green.
What is important when transitioning from 3 aspect signalling to 4 aspect signalling?
You must be aware that 3-aspect signalling cannot display preliminary caution. Thus, you could have a green from a 3-aspect signal, then a cautionary aspect at the 4 aspect.
What does an off indicator do?
An off indicator works in conjunction with the signal to which it applies. When the signal is cleared, the sign illuminates the word ‘OFF.’
Off includes proceed, caution, and preliminary caution. If the screen is blank, then the signal it corresponds to is displaying danger.
What is a SPAD indicator?
A SPAD indicator is provided at certain locations to indicate if a SPAD has occurred.
What happens when a SPAD indicator is lit?
If the SPAD indicator is lit, it indicates that a SPAD has occurred.
What does the SPAD indicator display when it goes off?
When the SPAD indicator goes off, the top and bottom will flash red, and the centre aspect will show a steady red.
What should a driver do if they see a SPAD signal go off?
The driver must stop the train immediately and contact the signaller as soon as possible.
What is the SPAD procedure?
The SPAD procedure must be carried out even if it is for another line.
What do right-away indicators display?
Right-away indicators display the letters ‘R’ or ‘RA.’
What does an illuminated right-away indicator signify?
If this indicator is illuminated, it tells the driver that station duties are complete, the train is secure, and it is safe to proceed.
