SIGNALS Flashcards
What is the principal of track circuit block working?
One train on on signal section on one line at any one time.
What is a stop signal?
Any signal capable of displaying a stop aspect or indication.
What is a signal section?
The distance between two stop signals.
What is a proceed aspect?
An indication that the next signal section is clear and can be passed into. This can be in the form of a yellow, two yellows, or green aspect for example.
Explain how two aspect signalling works.
Each signal is able to show two aspects, either green/red or yellow/green. Distant signals (repeaters) are used a braking distance between stop signals to indicate the need to slow or stop.
How would you distinguish a distant signal / repeater?
On the signal plate would have either a white arrow or the letter ‘R’ above the signal number.
Explain how three aspect signalling works.
Each signal can display green, yellow, or red and give service braking distance from yellow to red.
Explain how four aspect signalling works,
Each signal can display green, yellow, double yellow, or red and give service braking distance from double yellow to red.
What is a signal overlap?
The point at which one signal section ends and the next one starts is slightly in advance of a given signal. The distance between the signal and the actual point the signal section ends is called the overlap, which gives a small safety margin.
Explain axel counters and their advantages/disadvantages.
Alternative to track circuits, a counter is used to count the number of axels passing into a signal section and then counts them back out at the other end. This ensures a signal remains red even in the cases of a full derailment and is theoretically easier to repair. However, it is not possible to use safety measures such as TCOC’s on these running lines.
How would you identify a controlled, automatic and semi-automatic signal? What are the differences between them?
Automatic signal - White plate with horizontal black line through, changed by the passing of trains.
Semi automatic - as above, but also has the word ‘SEMI’ displayed on white board. Generally controlled by passing of trains, but may need to be controlled on occasion, such as into sidings.
Controlled - Just a typical black plate with signal number on location on. Controlled by a signaller and protect an aspect such as a crossing.
Describe a junction indicator.
White lights (5) on either the left or right of a signal, can be as many as three positions on each side. If illuminated and the signal is proceed, the junction indicated will be taken. If the signal is proceed and no route indicator is lit, then the train will remain on the current running line.
On the left is routes 1, 2 and 3. On the right is routes 4, 5 and 6 (from top to bottom).
Describe a route indicator.
A letter or number lit accompanying a proceed signal will indicate a specific route that the track is set for. This could be an ‘M’ for mainline, or a ‘3’ for platform three for example.
Explain when and why you might find a flashing double (or single) yellow aspect.
At a diverging junction on four (or three) aspect signalling to help give a train braking distance to a junction without having to stop it at the junction. This system effectively gives an extra signal section.
It follows flashing double yellow, flashing yellow, single yellow, red.
Describe a ground position light signal, shunt signal and position light signal associated with a signal.
Position light signals are capable of showing either…
1 - red (stop) or white (45 degrees, proceed)
2 - yellow (Stop unless going into shunt neck or siding with permission from shunter) or white (45 degrees, proceed).
These can alternatively be shunt signals, which have the same meaning but are disks which are either…
1 - A white disk with red band
2 - A black disk with yellow band.
Alternative ‘Position light signals’ can also be associated with a signal where they can only be off, or displaying two white lights at 45 degrees. These are used to indicate permissive working.
What is permissive working?
Where at a specific location you are allowed to proceed past a stop signal into an occupied section of track. Most commonly in cases of attachment.
What is a ‘POSA’? what does it look like and what action must you take?
A POSA is associated with a main signal aspect and when lit (flashing white lights) indicates that the given signal has failed. However, it also means that the track is set correctly for your train and that you may proceed at caution, obeying all other signals.
You do not need to contact signaller in these cases.
What is the principal of absolute block?
One train on one block section on one line at any one time.
What is a intermediate block signal? what is its purpose?
An intermediate block signal splits a block section with the use of a two aspect colour light signal. this allows the increased passage of trains through the section.
What is a subsidiary signal?
Used in semaphore signalling, a subsidiary signal indicates permission to conduct permissive working. They appear below a main aspect signal and appear as a red board with a horizontal white line through.
Describe a stacked route indicator (semaphore).
A stacked route indicator will read ‘top-to-bottom left-to-right’. With the highest of the semaphore boards referring to route 1, the second highest to route 2, and so on.
Describe a stepped route indicator (semaphore).
Stepped route indicators always indicate route 1, 2, 3 etc reading from left to right. They will step up or down in height, with the highest being the current running line.
What is a Limit of shunt indicator?
Only capable of showing a red stop signal, often shaped like a positional light signal. Often used for shunting moves when changing lines. Can only be passed with authority of signaller.
What is a stop board?
Usually found in yards and sidings, generally a simple white board with a red circle and ‘stop’ denoted on it. Often have an instruction such as ‘contact signaller’ or ‘await instruction’. Do not pass them without authority.
Describe the appearance and actions taken when a lit SPAD indicator is seen.
A blue signal with three red aspects found about 50 metres after a given junction. If illuminated, the driver must stop immediately even if the indicator is not on their line as the SPAD could have been by a train joining the same signal section.
How would you know a signal is not in use?
A white ‘X’ nailed onto a semaphore signal, or a black cover over a colour light signal, again with a white ‘X’ over it.
Describe the appearance and function of a banner repeater.
White circle with a black line on which gives and indication of the next signals aspect. Generally used in areas where a signal can be hard to see initially due to curvature of the line or rail infrastructure. They have ‘BR’ on their signal board along with the signal number of the signal they refer to.
If the line is horizontal then the following signal is on, if at 45 degrees then the signal is displaying a proceed aspect.
Tri-state banner repeaters can also show green instead of white to give further indication of the associated signal.
What are Co-acting signals?
These mirror an associated signal in locations where the main aspect may be hard to see. They may for example be on the ground.
They can be identified by the ‘CA’ letters on the signal plate.
What are preliminary route indicators?
Generally used in conjunction with banner repeaters, they indicate which route has been set ahead. Look like route indicators but instead of a letter or number show a letter in up to six directions.
Explain station ‘OFF’ indicators
When illuminated ‘OFF’ on a platform this indicates to staff that the platform starter signal is displaying a proceed aspect as the signal is ‘off’.
What are CD/RA indicators?
Used as staff dispatched platforms, CD indicates that station duties are complete and the doors can be closed, RA indicates that train is free to depart in relation to platform duties.
Describe what signage you would expect to see for a temporary speed restriction.
A temporary speed restriction warning board (yellow with flashing white lights) braking distance from the speed restriction and associated AWS 180m prior. A yellow temp speed board at the start of the speed and a ‘T’ (termination board) at the end.
Describe what signage you would expect to see for an emergency speed restriction.
An emergency speed indicator (with AWS 180m before) at least 400m before an emergency speed restriction warning board (yellow with flashing white lights) braking distance from the emergency speed restriction and associated AWS 180m prior. A yellow emergency temp speed board at the start of the speed and a ‘T’ (termination board) at the end.
What is a block section?
The area from the last signal controlled by a signal box to the first signal controlled by the next signal box.
