Signalling Flashcards
What is the principle of absolute block signalling?
One train, one section, one time to keep trains apart and avoid collisions.
What are the drawbacks of absolute block signalling?
Capacity can be limited
What type of signals are used in absolute block signalling?
Semaphore signals or colour lights
What does a semaphore distant signal at caution look like? What does this mean?
Yellow arm with fishtail in horizontal position with yellow light.
Be prepared to stop at the next stop signal- all associated stop signals will be at danger
What does a semaphore distant signal at clear look like? What does this mean?
Yellow arm with fishtail at 45 degrees with green light.
All associated stop signals will display proceed aspects.
What does a semaphore stop signal look like at danger? What does this mean?
Red horizontal arm with red light.
You must stop at this signal
What does a semaphore stop signal look like at proceed? What does this mean?
Red arm at 45 degrees with green light.
You may proceed past this signal.
Do you get AWS magnets before semaphore stop and distant signals?
Only 180m before semaphore distant signals. Not before stop signals.
What distance are distant signals from stop signals?
Service braking distance
What are your actions if the stop signal changes from danger to proceed after receiving a cautionary distant signal?
Proceed but expect the next stop signal to be at danger.
What are station limits?
The section between the signal box’s first signal (home signal) and last signal (section signal)
What is an absolute block section?
The section between Signal Box A’s station limits and Signal Box B’s station limits
OR
The section between the section signal in rear and the home signal controlled ahead
OR
The section between the intermediate block home in rear until the home signal ahead
Who controls absolute block sections?
The signal box ahead as they have to give permission to the previous signal box to allow trains into the absolute block section once the train ahead has been confirmed to have passed the clearance point of 400m beyond the home signal complete with tail lights
Why do trains have to fully pass the clearance point before trains can be allowed into the absolute block section?
To prevent the risk of collision if a train behind were to SPAD the home signal.
What is the purpose of checking for tail lamps?
To confirm that the train hasn’t divided and full train has left the section due to lack of track circuits
If there is only one signal within station limits, what does this signal serve as?
Both the home and section signal
If a distant signal and a stop signal are on the same post, who controls these?
The distant signal is controlled by the signal box ahead and the stop signal is controlled by the signal box at that location
Why would a distant signal and stop signal be placed on the same post?
Where there wouldn’t be service braking distance before the next stop signal.
If you receive an AWS warning before a post with both a distant and a stop signal on, what does this apply to?
The distant signal only but this doesn’t mean that the stop signal is clear.
If there is a junction within station limits, what may there also be?
More than one home signal
Where would these home signals be positioned and how would they work?
One home signal protecting the station on the main line and one home signal protecting the station on the junction- once the train arriving from the main line leaves the station, the signal on the junction can clear
Can there be more than one section signal?
There must only ever be one section signal per line within station limits
What is the purpose of intermediate block sections?
These shorten AB sections to increase capacity
What is the definition of an intermediate block section if there is 1 IB section?
From the section signal in rear to the intermediate block home ahead
What is the definition of an intermediate block section if there are 2 IB sections?
From the IB home in rear to the IB home ahead
Who controls IB sections?
The signal box in rear
How are trains detected in IB sections?
Track circuits
What type of signals are used in IB sections?
Colour light signals only
Are there AWS magnets before IB signals?
Yes, 180m before them.
Do IBH signals have distant signals before them?
Yes.
How would you identify a colour light distant signal?
Triangle or ‘R’ on ID plate.
What are semaphore subsidiary signals?
A subsidiary arm that is associated with the main arm of a stop signal and located below on the same post.
What is meant if the main arm is at danger (horizontal with red light) and the subsidiary arm is horizontal?
Obey the main arm
What is meant if the main arm is at danger and the subsidiary arm is at 45 degrees with green light?
Proceed past the main arm at danger and prepare to stop short of BOTS
What is meant if the main arm is at danger and the subsidiary arm is at 45 degrees with the letter ‘C’?
Calling on- entering a platform permissively- proceed at caution and prepare to stop short of BOTS
What is meant if the main arm is at danger and the subsidiary arm is at 45 degrees with the letter ‘S’?
Shunt ahead- proceed for shunting purposes only (proceed at caution and prepare to stop short of BOTS)
What is meant if the miniature arm is offset from the main signal?
It is a shunting signal- when cleared, proceed at caution and be prepared to stop short of BOTS.
How does semaphore stepped routing work?
Left to right- furthest left signal for the route on the extreme left
Highest step is the highest speed route
Equal steps are equal speed routes
How does semaphore stacked routing work?
Top to bottom, left to right (not based on speed). Top signal applies to furthest left route.
How does semaphore route indicator routing work?
Figure or letter displayed to correspond with the route the move is signalled onto.
If the main arm is at danger, the route indicator is unlit. The arm is the authority to proceed, not the route indicator but both must be correct to proceed.
What are non-block signals?
Signals that do not control the movement of trains- their only purpose is to protect a level crossing and they are controlled by a crossing keeper or signaller.
What would you expect to see if a non-block crossing fails?
A green hand signal as authority to pass over a crossing if the non-block signal protecting the crossing fails. This tells you that the crossing is safe and you have permission to pass the signal at danger.
How do you find out the locations of non-block crossings?
In the Sectional Appendix
What are your actions if a green hand signal is shown at other locations?
Only the crossing is safe but you do not have permission to pass the protecting signal. You must wait for the signal to clear before proceeding.
How are semaphore distant signals replaced?
2 aspect colour lights (yellow/green) with ‘R’ or triangle on ID plate
How are semaphore stop signals replaced?
2 aspect colour lights (Red/green)
When semaphore stop signals are replaced, do they still serve as home and section signals?
Yes
When semaphore signals are replaced with colour lights, does this mean that track circuits are also present?
No
When semaphore stop signals are replaced with colour lights, do they get fitted with AWS magnets?
No, you still won’t receive AWS warnings for stop signals
What is the default position of semaphore signals?
Horizontal until cleared (fail safe)
At what point can distant signals clear?
When all associated stop signals have cleared first
How must you always treat the next stop signal?
Based on what the distant is showing, even if you see the stop signal ahead to be clear.
If you are expecting to work permissively but cannot see another train, what does this mean?
The train has already left and the proceed signal doesn’t apply to you. Wait for the signal to show danger and clear again.
What are your actions if you are unsure of the aspect shown?
Treat as most restrictive and contact signaller.
If the distant signal shows a proceed aspect but you receive an AWS horn, what are your actions?
Treat as cautionary unless the signal clears after passing the AWS magnet or if there is a warning board/emergency indicator positioned at the signal.
