British railway signals
Encyclopedia
Modern British signalling is based on a two, three, and four aspect colour light system using non-permissive block rules. It is a basic progression of the original semaphore signalling
that can still be found on many secondary lines. The use of lineside signals in Britain is restricted to railways with a maximum permissible speed of up to 125 mph (201.2 km/h).
lines. Current British practice mandates that semaphore signals, both upper and lower quadrant types, are inclined at an angle of 45° from horizontal to display an off indication.
A stop signal comprises a red arm with a square end and a white band. In the horizontal position, the meaning is stop (red light at night). When the arm is inclined, the meaning is proceed (green light at night). A distant signal comprises a yellow arm with a fishtailed end and a black chevron. In the horizontal position, the meaning is caution (yellow light at night). When the arm is inclined, the meaning is proceed (green light at night). When stop and distant arms are mounted together on one post, the stop arm is positioned above the distant arm.
Preliminary caution (double yellow): Be prepared to find the following signal showing caution (yellow).
Caution (yellow): The following signal will be showing Stop (red), and the driver must be prepared to stop at the following signal if it does not change to a less restrictive aspect before they reach it.
Stop (red):
Signals which display whether the route is diverging from the route ahead will have a Route Indicator—colloquially called a feather—of white lights (originally a single, long, u-shaped fluorescent tube in an open-fronted case) attached to the main signal.
If the feather is lit, then the train will be diverging from the main route at the next junction
. A feather can point to the left or to the right, as appropriate.
A signal has more than one feather where there is more than one diverging route ahead. The lit feather indicates which diverging line the train will be directed to. In the example shown, there are two routes diverging to the left of the main line, and the train will take the first one of the two.
In areas where speeds are lower, and there are a number of routes which can be taken, alphanumeric (also called theatre-style) route indicators are used to display a number or a letter to denote the route the train is to take (e.g., a platform number or line designation). They may located above or beside the relevant signal. When a route is set and the signal is cleared, the relevant letter or number is shown. On shunting signals, where speeds are much lower, a miniature version of the alphanumeric route indicator is used.
When a route is set at a junction that involves the train taking a diverging route that must be passed at less than the mainline speed, a system known as approach release is used. There are a number of different types of approach release that are used on British railways but the most often used is approach release from red. This system has the signal before the diverging junction held at red until the train approaches it, whereupon it changes to a less restrictive aspect with the appropriate direction feather of five white lights. This is required so that the signals approaching show the correct caution aspects, slowing the train down for the junction. While the junction signal is held at red, the preceding signal will be displaying caution (yellow), and the one before that will display preliminary caution (double yellow) if it is a 4-aspect signal. This system allows for a gradual decrease in speed until a safe speed is reached for the train to move through the junction.
Another common system is approach release from yellow with flashing aspects in rear. It is essentially similar to approach release from red, except that the junction signal is released from yellow and the signals in rear will flash to warn the driver that the train will be taking a diverging route ahead.
Where the turnout speed is the same as the mainline speed, approach release is not necessary.
On modern high speed routes, such as the East
and West
Coast Main Lines, some turnouts at major junctions are designed to operate at maximum or near maximum linespeeds to keep the average speed of the journey as high as possible and reduce journey times as well as unnecessary wear on the train wheels, brakes and the track. Movable frog switches
are occasionally employed to allow high speed running through the junction.
Banner on: The signal being repeated is showing a Stop aspect, and the train must be prepared to stop at that signal.
Banner off: The signal being repeated is showing a proceed aspect, so can be passed.
Green banner: Although not in widespread use, some banner repeaters can display a third (green) indication, meaning that the signal being repeated is showing a Clear aspect.
signals allow a train to move forward onto a line which may already be occupied.
These signals may also be placed on the ground called a ground position light (GPL), or on a post with no corresponding main signal. In this case, the signals will show either two red lights or a red and white light in a horizontal arrangement, when no movement is signalled.
If two red lights or one red and one white are shown, the signal must not be passed.
When a shunting movement is signalled, the signal will show two white lights in a diagonal arrangement. This means the driver may pass the signal with caution at a speed which allows the train to stop at any obstruction.
This type of signal is also used to designate a limit of shunt, the point up to which trains that are shunting are allowed to proceed. In this case, two red lights are displayed side by side, but no other aspect can be shown. No train is allowed to pass this fixed signal in the direction shown (this will be against the normal direction of travel on the track in question).
Here the two yellow lights or one yellow one white indicate a shunting movement is permitted past the signal but only for a move in a direction for which the signal cannot be cleared (for example, towards a headshunt rather than on to the main line). Again, two white lights at a 45° angle indicate shunting is permitted.
Off Indicator: An illuminated off indication means the associated signal is showing a proceed aspect. These are mainly used at stations, for the benefit of the train-crew and platform staff. When the display is blank, it means that the associated signal is at danger.
An illuminated indication CD (close doors) is an instruction to close the train's power-operated doors.
An illuminated indication RA or R (right away) means that station duties are complete and the train may depart.
s, certain junctions
, tunnels and bridges and where the train is entering a terminal station
.
Warning boards
Warning of a permanent speed restriction (PSR) ahead of 75 mph (120.7 km/h). Typically placed about a half mile to a mile before the start of the permanent speed restriction, depending upon the difference between the maximum permitted line speed and the restricted line speed.
Warning of a permanent speed restriction on the left diverging route of 75 mph (120.7 km/h). Again, typically placed about a half mile to a mile before the permanent speed restriction on the diverging route, depending upon the difference between the maximum permitted line speed and the restricted line speed.
Permanent speed restriction signs
Start of permanent speed restriction of 125 mph (201.2 km/h) on the main route
Start of differential permanent speed restriction, with two varying restrictions for different types of trains. The figure above the line is the maximum permitted speed for freight trains, while the figure under the line is the maximum line-speed for passenger trains. In this example, freight is permitted to 35 mph (56.3 km/h), while passenger trains are permitted to 70 mph (112.7 km/h).
Start of permanent speed restriction of 40 mph (64.4 km/h) on the diverging route to the left. Placed before the diverging route to instruct or remind the driver of the maximum line speed on the diverging route.
Warning of temporary speed restriction of 40 mph (64.4 km/h) ahead.
The start and termination indicators of a temporary speed restriction of 40 mph (64.4 km/h).
A temporary speed restriction warning board showing R is positioned beyond the end of platforms where trains may stop between the warning board and the start of the restriction, to remind drivers of the restriction ahead. A warning or commencement board showing a diagonal line means that a TSR shown in the operating notices is not in place and trains may proceed at normal line speed.
electric locomotives following the electrification of the East Coast Main Line
in the late 1980s, British Rail
introduced a flashing green aspect as authority to exceed 125 mph (201.2 km/h) (up to a maximum of 140 mph (225.3 km/h)) on the stretch between Stoke Junction, south of Grantham, and Werrington Junction, north of Peterborough. These aspects do not apply to trains running in normal service.
Meaning: The track ahead is clear and available for running in excess of 125 mph (201.2 km/h). The train is permitted to travel at a speed in excess of 125 mph (201.2 km/h), up to the current line limit (which may be as high as 140 mph (225.3 km/h)). The following signal will be showing clear (green or flashing green). Although the signals show a flashing green aspect, drivers are still not allowed to exceed 125 mph (201.2 km/h), and thus this system is not in use.
Railway semaphore signal
One of the earliest forms of fixed railway signal is the semaphore. These signals display their different indications to train drivers by changing the angle of inclination of a pivoted 'arm'. Semaphore signals were patented in the early 1840s by Joseph James Stevens, and soon became the most...
that can still be found on many secondary lines. The use of lineside signals in Britain is restricted to railways with a maximum permissible speed of up to 125 mph (201.2 km/h).
Semaphore signal indications
Semaphore signals exist in both lower quadrant and upper quadrant forms. Both types have the same meanings. From the 1920s onwards, upper quadrant semaphores almost totally supplanted lower quadrant signals in Great Britain, except on former GWRGreat Western Railway
The Great Western Railway was a British railway company that linked London with the south-west and west of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament in 1835 and ran its first trains in 1838...
lines. Current British practice mandates that semaphore signals, both upper and lower quadrant types, are inclined at an angle of 45° from horizontal to display an off indication.
A stop signal comprises a red arm with a square end and a white band. In the horizontal position, the meaning is stop (red light at night). When the arm is inclined, the meaning is proceed (green light at night). A distant signal comprises a yellow arm with a fishtailed end and a black chevron. In the horizontal position, the meaning is caution (yellow light at night). When the arm is inclined, the meaning is proceed (green light at night). When stop and distant arms are mounted together on one post, the stop arm is positioned above the distant arm.
Colour light signal aspects
Clear (green):The track ahead is clear. The train is permitted to travel at any speed up to the current line limit.
If the signal is a 4-aspect signal, then the following signal will be showing clear (green) or preliminary caution (double yellow). If the signal is a 3-aspect signal, then the following signal will be showing clear (green), or caution (yellow).
Preliminary caution (double yellow): Be prepared to find the following signal showing caution (yellow).
Caution (yellow): The following signal will be showing Stop (red), and the driver must be prepared to stop at the following signal if it does not change to a less restrictive aspect before they reach it.
Stop (red):
Also known as danger. The driver must stop at the signal. The train may only proceed when the signal changes to a less restrictive aspect.
The red stop signal is non-permissive and must not be passed. This signal denotes that the block ahead is occupied and must not be entered for safety reasons. Additionally, a red signal will be shown on the approach to a set of pointsRailroad switchA railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track to another at a railway junction....
when a clear path through them is not set.
Junction signals
British signalling is unusual in that when a train approaches a junction and is taking a diverging route, the preceding signal will indicate the diverging route to the driver. A fixed lineside sign shows the speed that applies through the divergence. Most signalling systems around the world adopt the speed signalling philosophy, where the safe route speed is shown with no indication of the divergence at a junction.Signals which display whether the route is diverging from the route ahead will have a Route Indicator—colloquially called a feather—of white lights (originally a single, long, u-shaped fluorescent tube in an open-fronted case) attached to the main signal.
If the feather is lit, then the train will be diverging from the main route at the next junction
Junction (rail)
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge.This implies a physical connection between the tracks of the two routes , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...
. A feather can point to the left or to the right, as appropriate.
A signal has more than one feather where there is more than one diverging route ahead. The lit feather indicates which diverging line the train will be directed to. In the example shown, there are two routes diverging to the left of the main line, and the train will take the first one of the two.
In areas where speeds are lower, and there are a number of routes which can be taken, alphanumeric (also called theatre-style) route indicators are used to display a number or a letter to denote the route the train is to take (e.g., a platform number or line designation). They may located above or beside the relevant signal. When a route is set and the signal is cleared, the relevant letter or number is shown. On shunting signals, where speeds are much lower, a miniature version of the alphanumeric route indicator is used.
When a route is set at a junction that involves the train taking a diverging route that must be passed at less than the mainline speed, a system known as approach release is used. There are a number of different types of approach release that are used on British railways but the most often used is approach release from red. This system has the signal before the diverging junction held at red until the train approaches it, whereupon it changes to a less restrictive aspect with the appropriate direction feather of five white lights. This is required so that the signals approaching show the correct caution aspects, slowing the train down for the junction. While the junction signal is held at red, the preceding signal will be displaying caution (yellow), and the one before that will display preliminary caution (double yellow) if it is a 4-aspect signal. This system allows for a gradual decrease in speed until a safe speed is reached for the train to move through the junction.
Another common system is approach release from yellow with flashing aspects in rear. It is essentially similar to approach release from red, except that the junction signal is released from yellow and the signals in rear will flash to warn the driver that the train will be taking a diverging route ahead.
Where the turnout speed is the same as the mainline speed, approach release is not necessary.
On modern high speed routes, such as the East
East Coast Main Line
The East Coast Main Line is a long electrified high-speed railway link between London, Peterborough, Doncaster, Wakefield, Leeds, York, Darlington, Newcastle and Edinburgh...
and West
West Coast Main Line
The West Coast Main Line is the busiest mixed-traffic railway route in Britain, being the country's most important rail backbone in terms of population served. Fast, long-distance inter-city passenger services are provided between London, the West Midlands, the North West, North Wales and the...
Coast Main Lines, some turnouts at major junctions are designed to operate at maximum or near maximum linespeeds to keep the average speed of the journey as high as possible and reduce journey times as well as unnecessary wear on the train wheels, brakes and the track. Movable frog switches
Swingnose crossing
A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.- Fixed crossing :...
are occasionally employed to allow high speed running through the junction.
Banner repeater signals
Banner repeater signals repeat the indication of the following signal, where the driver's view of it may be restricted, for example because of track curvature or a bridge abutment.Banner on: The signal being repeated is showing a Stop aspect, and the train must be prepared to stop at that signal.
Banner off: The signal being repeated is showing a proceed aspect, so can be passed.
Green banner: Although not in widespread use, some banner repeaters can display a third (green) indication, meaning that the signal being repeated is showing a Clear aspect.
Shunting signals
ShuntingShunt (railway operations)
Shunting, in railway operations, involves the process of sorting items of rolling stock into complete train sets or consists. The United States terminology is "switching"....
signals allow a train to move forward onto a line which may already be occupied.
Position light signals
Shunting signals may be attached to a main signal in which case they are only cleared when the shunting movement is required (known as a subsidiary signal), and they display two white lights at an angle of 45°. The driver may pass the signal with caution at a speed which allows the train to stop short of any obstruction.These signals may also be placed on the ground called a ground position light (GPL), or on a post with no corresponding main signal. In this case, the signals will show either two red lights or a red and white light in a horizontal arrangement, when no movement is signalled.
If two red lights or one red and one white are shown, the signal must not be passed.
When a shunting movement is signalled, the signal will show two white lights in a diagonal arrangement. This means the driver may pass the signal with caution at a speed which allows the train to stop at any obstruction.
This type of signal is also used to designate a limit of shunt, the point up to which trains that are shunting are allowed to proceed. In this case, two red lights are displayed side by side, but no other aspect can be shown. No train is allowed to pass this fixed signal in the direction shown (this will be against the normal direction of travel on the track in question).
Here the two yellow lights or one yellow one white indicate a shunting movement is permitted past the signal but only for a move in a direction for which the signal cannot be cleared (for example, towards a headshunt rather than on to the main line). Again, two white lights at a 45° angle indicate shunting is permitted.
Miscellaneous indicators
An illuminated indication CD (close doors) is an instruction to close the train's power-operated doors.
An illuminated indication RA or R (right away) means that station duties are complete and the train may depart.
Speed restriction signs
Speed restrictions are imposed on a route to ensure a train is always travelling at a safe speed for the prevailing conditions along the track.Permanent speed restrictions
Permanent speed restrictions are imposed where the route encounters a hazard such as a tight radius curve, level crossingLevel crossing
A level crossing occurs where a railway line is intersected by a road or path onone level, without recourse to a bridge or tunnel. It is a type of at-grade intersection. The term also applies when a light rail line with separate right-of-way or reserved track crosses a road in the same fashion...
s, certain junctions
Junction (rail)
A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge.This implies a physical connection between the tracks of the two routes , 'points' and signalling.one or two tracks each meet at a junction, a fairly simple layout of tracks suffices to...
, tunnels and bridges and where the train is entering a terminal station
Terminal Station
Terminal Station is a 1953 film by Italian director Vittorio De Sica. It tells the story of the love affair between an Italian man and an American woman. The film was entered into the 1953 Cannes Film Festival.-Production:...
.
Warning of a permanent speed restriction (PSR) ahead of 75 mph (120.7 km/h). Typically placed about a half mile to a mile before the start of the permanent speed restriction, depending upon the difference between the maximum permitted line speed and the restricted line speed.
Start of permanent speed restriction of 125 mph (201.2 km/h) on the main route
Temporary speed restrictions
Due to engineering works, a temporary speed reduction (TSR) may be enforced at a particular location.A temporary speed restriction warning board showing R is positioned beyond the end of platforms where trains may stop between the warning board and the start of the restriction, to remind drivers of the restriction ahead. A warning or commencement board showing a diagonal line means that a TSR shown in the operating notices is not in place and trains may proceed at normal line speed.
Flashing green
During testing of the Class 91British Rail Class 91
The British Rail Class 91 is a class of , electric locomotives ordered as a component of the East Coast Main Line modernisation and electrification programme of the late 1980s. The Class 91s were given the auxiliary name of InterCity 225 to indicate their envisaged top speed of...
electric locomotives following the electrification of the East Coast Main Line
East Coast Main Line
The East Coast Main Line is a long electrified high-speed railway link between London, Peterborough, Doncaster, Wakefield, Leeds, York, Darlington, Newcastle and Edinburgh...
in the late 1980s, British Rail
British Rail
British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...
introduced a flashing green aspect as authority to exceed 125 mph (201.2 km/h) (up to a maximum of 140 mph (225.3 km/h)) on the stretch between Stoke Junction, south of Grantham, and Werrington Junction, north of Peterborough. These aspects do not apply to trains running in normal service.
Meaning: The track ahead is clear and available for running in excess of 125 mph (201.2 km/h). The train is permitted to travel at a speed in excess of 125 mph (201.2 km/h), up to the current line limit (which may be as high as 140 mph (225.3 km/h)). The following signal will be showing clear (green or flashing green). Although the signals show a flashing green aspect, drivers are still not allowed to exceed 125 mph (201.2 km/h), and thus this system is not in use.
See also
- UK railway signallingUK railway signallingThe railway signalling systems used across the majority of the United Kingdom rail network use lineside signals to advise the driver of the status of the section of track ahead...
- InterlockingInterlockingIn railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant...
- Railway signalRailway signalA signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal's indication and acts accordingly...
- Railway signallingRailway signallingRailway signalling is a system used to control railway traffic safely, essentially to prevent trains from colliding. Being guided by fixed rails, trains are uniquely susceptible to collision; furthermore, trains cannot stop quickly, and frequently operate at speeds that do not enable them to stop...
- Signal boxSignal boxOn a rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable...
- Pass of Brander Stone SignalsPass of Brander stone signalsThe Pass of Brander stone signals are a series of railway signals situated in the Pass of Brander, between and stations on the Oban branch of the West Highland Line in Scotland. They are part of a warning system that advises train drivers to exercise caution in the event of a rock-fall.The...
- Signal passed at danger (SPAD)Signal passed at dangerA Signal passed at danger , in British railway terminology, occurs when a train passes a stop signal without authority to do so. It is a term primarily used within the British Railway Industry, although it can be applied worldwide.-Categories of SPAD:...