Signalling Changes 


A signalman or signaller is an employee of a railway transport network who operates the points and signals from a signal box in order to control the movement of trains.
The first signalmen, originally called Railway Policemen (leading to the nickname of 'Bobby'), were employed in the early 19th century and used flags to communicate with each other and train drivers, and  an hourglass for the purpose of Time Interval Working between stations.
It was a signalman's duty to check each train that passed his signal box, looking for the red tail lamp exhibited on the trailing vehicle, the sighting of which confirmed that the train was still complete, and thus the section was clear.
Each train movement was logged, by hand, in a Train Register Book, and it was normal practice to provide a special desk to support this sizeable book. As well as train movements, every communication between signalmen and adjacent signal boxes via bell codes (when accepting trains or dealing with a token) was logged.
Technological advances including mechanical fixed signals in the 1840s, the electric telegraph and block working in the 1850s, and proper mechanical interlocking from 1856, allowed safer, more expeditious train working, and more complicated track layouts to be controlled single-handedly. The advent of such technological advances gradually led to the provision of an enclosed workspace known as a signal box, signal cabin or interlocking tower.

With the invention of the electrical telegraph, it became possible for staff at a station or signal box to send a message (usually a specific number of rings on a bell) to confirm that a train had passed and that a specific block was clear. This was called the "absolute block system".

Fixed mechanical signals began to replace hand signals from the 1830s. These were originally worked locally, but it later became normal practice to operate all the signals on a particular block with levers grouped together in a signal box. When a train passed into a block, a 
signalman would protect that block by setting its signal to 'danger'. When an 'all clear' message was received, the signalman would move the signal into the 'clear' position. The absolute block system came into use gradually during the 1850s and 1860s and became mandatory in the United Kingdom after Parliament passed legislation in 1889 following a number of accidents. This required block signalling for all passenger railways, together with interlocking, both of which form the basis of modern signalling practice today. 

Not all blocks are controlled using fixed signals. On some single track railways in the UK, particularly those with low usage, it is common to use token systems that rely on the train driver's physical possession of a unique token as authority to occupy the line, normally in addition to fixed signals. 

                    Early Signalman

       A Victorian signalman at work 

                                                        Just one of the seven signal boxes at Rugby

Britain's current railway signalling is made up of a hotchpotch of different systems, many bolted on to much older technology. In some areas, sophisticated computer software controls train paths automatically, in others there are still signallers sitting in traditional wooden signal boxes pulling levers that connect to semaphore arms via a convoluted system of wires. An army of more than 3,000 signallers work around the clock, costing about £100m a year in wages.

Traditional signalling in Britain stems from a principle developed by the Victorians known as "block working". This is based on the principle of one train in each section at any time. But because these block sections are constrained by the fixed geography of the signals it is impossible to increase capacity.

ETCS replaces fixed signals altogether with digital "moving block" technology. In effect each train creates its own safety "buffer zone" by transmitting its actual positions in real time via a series of closely positioned track sensors known as balises. The system is similar to planes which use cockpit transponders to report their actual position to air traffic controllers when under radar coverage.

                                              Semaphore Signals 

 Under ETCS each train will transmit its exact position via the railway's own communications network to one of 12 new massive rail operating centres which will replace the 800 signal boxes currently in use. Computers will then work out the optimum distance between trains, taking into account their speed, braking distance and stopping patterns at stations.

It's hoped the new system will allow for much shorter headways between trains, resulting in a 40% increase in capacity. Reliability and journey times should also be improved as trains will not need to brake and accelerate as they do at present when bunching occurs as a result of fixed signals.

This technology is already in use on the high-speed TGV lines in France. On these dedicated routes trains travel at the same speed over long distances with few stops, making them the ideal test bed for the new technology. But getting the system to work on Britain's more complex 100-year-old existing network will be a far greater challenge for engineers.

       The control used by controllers to set routes

                                                               Route Operating Centre     photo¬©NetworkRail

Network Rail, the company which manages the UK's rail infrastructure, is replacing the remaining 800 signalling locations with 14 Route Operating Centres and reducing the signalling workforce by two-thirds, to 2,000 as part of an overhaul of the system. The project is expected to take up to 30 years and will cover England, Wales and Scotland.

About 80% of the new system is estimated to be in place within the next 15 years. As part of the overhaul, English Heritage has carried out a review of operational signal boxes and those in heritage railways and museums in England to identify those boxes that might be worth preserving. Fortunately, many signal boxes are readily moveable, and have either been relocated to heritage railways, or taken for other uses - artists' studios, club houses, garden sheds or museums. So it will remain possible to see these structures doing what they were designed for, or as part of a community's assets, long after Network Rail's need for them is over.