What are railway signal boxes and why are they necessary?

Image removed.
Photo-montage showing
the extant signal boxes
within the SCRCA
as of October 2012.

To view a larger version,
click / tap on the thumbnail.

What are signal boxes?

Signal boxes are shelters or small buildings constructed specifically to:

  • house the levers and other control equipment used to safely space, route and locally coordinate railway trains; and to
  • provide signalling staff with a vantage point from which to safely observe and efficiently control nearby trains.

Why are signal boxes necessary?

The short answer (kindly supplied by Dave Harris) is:

"to maintain a safe separation of trains and to facilitate shunting".

The more detailed answer involves a whistlestop journey through railway history and the key principles of railway operations.

1: Train drivers can't steer their trains

Trains run on (and are steered by) a pair of parallel rails laid on the ground. This means that they cannot steer round one another like road vehicles can. In places where trains need to pass one another (or to change from one route to another), points are installed and these need to be operated carefully to avoid derailments and collisions.

2: Keeping trains safe is harder when things get fast, busy or both

On slow-speed routes with just one train in operation, train crews can stop at points and use an adjacent lever to set the points for the route they want to take. This practice works reasonably well for small-scale industrial railway systems and for shunting in small goods yards, etc. However, for long-distance routes, large industrial complexes and major goods yards, this procedure is highly inefficient. Also, coordinating the trains becomes difficult if more than one train is operating in a given area. Furthermore, as the number and speed of trains increases, so does the risk of a collision.

3: To avoid collisions, rules and procedures are needed

During the early years of railway operations (more than thirty years before the Settle-Carlisle line was constructed), a series of rules and operating procedures were introduced to help things run efficiently (and, with luck, safely). For example:

  • Trains theoretically operated to fixed timetables and there was a fixed minimum time interval between trains using the same line. (For the Midland Railway in the 1840s, the minimum time interval was ten minutes.)
  • Train drivers were required to maintain a minimum distance from the train in front at all times. (For the Midland Railway in the 1840s, the minimum distance was 800 yards.) Train drivers were also required to adhere to the prescribed timetable.
  • A 'pointsman' was stationed at each important set of points to ensure that they were set correctly for each train.
  • Policemen were assigned to key locations to enforce the rules regarding train separation and safe operation.

4: To avoid collisions, train drivers need information

Initially, the railway policemen used hand, flag or lamp signals to tell drivers when to stop and when it was time (and theoretically safe) to depart. This activity is depicted in the engraving of Derby station below, where the man wearing a top hat (bottom-right corner) is holding a flag.

Derby Station on the North Midland Railway circa 1840
A railway policeman uses a flag to 'signal' instructions to a train driver
Black and white engraving showing a railway policeman signalling to a train driver at Derby station.

Unfortunately, these early signalling techniques could be difficult to see - or to interpret correctly from a distance - and this caused a number of accidents.

In a bid to overcome this problem, various designs of pole-mounted signal boards were introduced. These were known as 'semaphore signals' and some of the Midland Railway Company's early designs can be seen in the four illustrations below. (Tip: As the signals only form a small part of each image, you may wish to click- or tap-on each image in turn to view a larger version.)

Examples of early Midland Railway Company semaphore signals
Source: Williams, F.S.: "The Midland railway: its rise and progress. A narrative of modern enterprise" (1876)
Black & White lithograph showing early railway signals near Ambergate Tunnel on the Midland Railway. Black & White lithograph showing early railway signals near Bull Bridge on the Midland Railway.
Black & White lithograph showing early railway signals at Trent Station on the Midland Railway. Black & White lithograph showing early railway signals at Clay Cross Junction on the Midland Railway.

In each case, the position of the signal board, ball or arm indicated whether or not it was safe for the train to proceed. Over the years, each railway company developed and refined its own standard design for these semaphore signals. The drawing below shows the Midland Railway Company's standard design for signals between circa 1880 and circa 1910.

Drawing showing the Midland Railway Company's standard design for signal arms

However, there was still a place for hand signals long after the development of post-mounted semaphore signals. (This is illustrated in the drawing of Clay Cross Junction above. Note the signalman with a flag standing on top of the signalling tower, even though there are two prominent post-mounted semaphore signals next to - and accessible by ladder from - the tower.)

Examples of railway signalling from an 1876 edition of the Midland Railway Company Rulebook
Danger Signal: Both arms raised above the head denotes “Danger”. Caution Signal: One arm raised above the head denotes "Caution".
All Right Signal: One arm held in a horizontal position across the Line of rails denotes “All Right”. Semaphore Danger Signal: The Danger Signal is shown, in the day time, by the Arm on the left hand side of the post being raised to the horizontal position . . . and by the exhibition of a red light by night.
Semaphore Caution Signal: The Caution Signal is shown, in the day time, by the Arm on the left hand side of the post being placed half-way to the horizontal position . . . and by the exhibition of a green light by night. Semaphore All Right Signal: The All Right Signal is shown, in the day time, by the Arm on the left hand side being lowered to the post . . . and by the exhibition of a white light by night.

5: Railway policemen handed over to railway signalmen

In some parts of the railway network, the responsibility for operating the signal boards was gradually transferred to station staff. Eventually, the policemen or station staff performing these 'signalling' duties became known as 'signalmen'.

6: As capacity increased, so did the costs

Initially, pointsmen operated the points via an adjacent lever and signalmen operated the semaphore signals via a lever located at the base of each signal.

As the number of points and signals increased, the number of pointsmen and signalmen also increased. One person was needed for each point or signal and this began to make operating the railways very expensive. It was also very dangerous to have people standing beside the track and there were a number of incidents where pointsmen and signalmen were hit by moving trains.

7: When things get busy, someone needs to take control

At busy locations (such as stations and junctions), it was very difficult to coordinate the operation of points and signals located hundreds of yards apart. A signalman could tell the driver it was safe to proceed before all of the pointsmen had correctly set their points. The solution to this problem was to bring the levers together in a single location, which enabled them to be operated by one person. The railway companies liked this idea because it improved coordination and safety, while also saving money on labour costs.

8: Things (and people) work better when they are kept warm and dry

To protect all this expensive equipment from the weather, it was placed inside small buildings that were specially designed to provide the signalmen with good visibility.

And so the railway signal box was born.

There was another (largely incidental) benefit to these buildings: they gave signalmen somewhere relatively warm and dry to work.

9: Despite all this, people can still make mistakes

The Hawes Junction Disaster (1910)

At about 5:19 a.m. on Saturday, 24th December 1910, twelve people died and thirty were injured when the midnight express from London St. Pancras to Glasgow ploughed into the back of a pair of slow-moving locomotives approximately one and a half miles north of Hawes Junction (Garsdale).

The official Board of Trade accident report paints a vivid picture of the disaster: "the two front coaches of the express telescoped, and were completely wrecked. Fire broke out, immediately after the collision, in these two vehicles, and eventually all the coaching stock on the train, with the exception of the two rear brake vans, was burnt."

B&W photo showing two derailed locomtives, partially on their sides and the wreckage of the two leading carriages.

The Board of Trade inspector concluded that "responsibility for this accident rests upon signalman Sutton, in that he took no action to remind himself of the position of the Carlisle engines, and did not assure himself by observation that the line was clear before allowing the express to approach."

The inspector also assigned blame to the crews of the two light engines because "they did not try to attract Sutton's attention by whistling, nor did they in accordance with Rule 55 send back one of their firemen to the signal-box to remind him of their position."

Human error is one of the biggest causes of accidents and even carefully selected and well trained people can make mistakes, especially when they are overworked, tired, distracted, overconfident and / or careless. Mistakes by railway signalmen can have particularly devastating consequences and the lessons learned from accidents have resulted in a number of key improvements to both signalling equipment and the associated operating procedures.

During the middle decades of the 19th century, a desire to reduce the scope for human error led to the development and widespread introduction of two of the most important innovations in early railway signalling technology:

  • lever frames with mechanical interlocking (to prevent local points and signals being set in a confusing or conflicting manner); and
  • the block telegraph system (to improve communication and coordination between adjacent signal boxes).

It is no coincidence that the widespread introduction of railway signal boxes occurred at broadly the same time as the widespread adoption of these two technological innovations.

Unfortunately, despite these improvements, human error could (and still can) lead to horrific accidents. One of the best-known accidents on the Settle-Carlisle Railway occurred in 1910 between Hawes Junction and Ais Gill Summit (see inset). Fortunately, lessons learned from railway accidents like this one have led to further improvements in both railway equipment and operating procedures. As a result, travelling by train is now far safer than travelling by road.

The future of signal boxes

In 1948, there were approximately 10,000 signal boxes in Great Britain. By 2012, this had been reduced to less than 500 and the number is falling every year. This dramatic nationwide reduction is the result of the rationalisation of the railway network, developments in electrical / electronic control systems and improvements in communications technology. One of the most visible changes across most of Britain's mainline rail network is the replacement of semaphore signals with coloured light signals. (These are easier to see in the dark and in fog and they can be controlled from much further away.)

Despite these changes at a national level, there are still nine traditional signal boxes in operational use within the SCRCA (plus one 'powerbox' dating from 1973 and one portacabin installed in 1994). Although this is a significant reduction from the peak of 41 traditional signal boxes, it does mean that most of the railway between Hellifield and Carlisle is still controlled by traditional signalling equipment (see photographs below for examples).

Examples of signalling equipment in the Settle-Carlisle Railway Conservation Area today
Photo: The ground frame for Ribblehead Quarry Siding.
The ground frame for
Ribblehead Quarry Siding
Photo: A typical Midland Railway Company lever frame and block instruments.
A typical Midland Railway Company
lever frame and block instruments.
Photo: Appleby Junction, featuring points, semaphore signals and the signal box that controls them.
Appleby North Junction, with points,
semaphore signals and signal box

However, under current plans, the whole of Britain’s national rail network will eventually be controlled from just 14 "rail operating control centres". While the traditional signal boxes within the Settle-Carlisle Railway Conservation Area are likely to be among the last to be decommissioned, they will almost certainly become redundant over the next twenty years or so. On a brighter note, two of the line’s signal boxes (Settle Station and Armathwaite) have already been preserved and these now house small museums that are open to the public. The future of the other signal boxes is less certain, but it is hoped that at least one more (Garsdale) can be preserved to help tell the fascinating story of signal boxes and signalling within SCRCA.

Further reading

Additional information relating to the nine remaining traditional signal boxes within the SCRCA can be accessed via the following 'virtual visit' page:

The official Board of Trade report into the 1910 Hawes Junction disaster can be viewed and / or downloaded in pdf format via the following link:

The following online sources provide a wealth of background information relating to the design, manufacture, purpose and operation of signal boxes and the signals that they operate:


Text by Mark R. Harvey (© Mark R. Harvey, 2017). Illustrations supplied by Mark R. Harvey and Dave Harris. The author would like to thank Dave Harris for his assistance with this article and for providing many of the images. This article could not have been written without Dave's extensive knowledge of signalling history, practices and procedures.

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