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Railway semaphore signal
Railway semaphore signals are an early form of fixed railway signals. The semaphore system involves signals that 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 widely used form of mechanical signal. Designs have altered over the intervening years, and colour light signals have replaced semaphore signals in most countries, but in a few they remain in use.
The first railway semaphore signal was erected by Charles Hutton Gregory in about 1842, on the London and Croydon Railway (later the London Brighton and South Coast Railway) at New Cross, southeast London, as part of the newly enlarged layout also accommodating the South Eastern Railway. John Urpeth Rastrick claimed to have suggested the idea to Hutton Gregory.
The semaphore was swiftly embraced across Britain and North America as a fixed manual signalling system, surpassing all other types in most applications by 1870. Becoming electrically operated and automatic, accompanied by interlocking, they were widely adopted in the U.S. After 1908, with the advent of the Union Switch & Signal types "B" & "S", and the General Railway Signal Company's universal Model 2A mechanisms, manual semaphores and earlier electric disc signals quickly began to disappear.
The British semaphore signal arm consists of two parts: A wooden or metal arm (or "blade") which pivots at different angles, and a spectacle holding coloured lenses which move in front of a lamp in order to provide indications at night. Usually these were combined into a single frame, though in some types (e.g. "somersault" signals in which the arm pivoted in the centre), the arm was separate from the spectacle. The arm projects horizontally in its most restrictive aspect; other angles indicate less restrictive aspects. On double lines in Great Britain signal posts are generally placed on the left of the track and always with the semaphore arm(s) facing left with the spectacle and lamp on the right of the post or doll (but on the left of the post or doll for upper-quadrant signals). Sighting problems may mean that the post is placed on the right of the other line on double track branches and on single lines, could be placed either side of the track. North American semaphore equivalents faced right, and as generally on the European continent, on double track branches, up and down lines are opposite to those in the UK.
Depending on the arm's position, the appropriately coloured lens is illuminated from behind by either an oil lamp, a gas lamp, or an incandescent lamp run at a low voltage (white LED clusters have also been tested for this purpose). Where a green light was required, a blue lens would usually be used. When combined with the mainly yellow-emitting flame of an oil lamp, this produced a green colour; it was important that the resultant colour was not even yellow-green in appearance, as this could have been confused for a distant signal at 'caution'. Later signals using electric lamps used green lenses. Some signals converted to electric lamps from oil, used a yellow-tinted bulb with the original blue lens to maintain the correct colour or from 1996 on the Western Region of British Railways, a 12-volt 5-watt bulb was fitted but fed at 10.7 volts to produce a brilliance approximating to the colour temperature of an oil wick flame, thus providing a correct red or green aspect during darkness. Most railways in Great Britain employed lower-quadrant semaphores, where the arm dropped from the horizontal 'danger' aspect to 'clear' at up to 60° below horizontal. Variations in appearance between main and subsidiary lines or sidings also existed. On some company's lines, a three-aspect semaphore prevailed and these showed an intermediate 'Caution' aspect and thus bore a three-lensed spectacle. In 1911, the Metropolitan Line was first to use an upper-quadrant semaphore, the idea being brought over from the United States. Following nationalisation in 1948, British Railways standardised on upper-quadrant semaphores and all regions gradually adopted that mode, replacing lower-quadrant signals. However, the Western Region stayed with their well-proven lower-quadrant semaphores, with a heavy cast iron spectacle bearing circular coloured glasses eventually replacing the former thinly bordered cast spectacle frame with shaped coloured glasses. The main arms were 4 feet (1.2 m) long and subsidiaries 3 feet (0.91 m) with other subsidiaries 2 feet (0.61 m) long on these signals. Previous GWR 5-foot (1.5 m) arms placed if higher than 26 feet (7.9 m) above rail level, were changed to 4 feet (1.2 m). All replacements were of enamelled steel and bore the appropriate arm colours, red with white band for 'Stop' arm and chevroned yellow arm with black chevron for 'Distant' (Caution) arms. Both types are white on the reverse side with black band or chevron as appropriate. The final 'Call-on', Shunt' or 'Warning' arms on the Western Region were 2 feet (0.61 m) with red-white-red horizontal stripes and showed a reduced light during darkness with the appropriate black letter, C, S or W, back-lit in the 'proceed' state with a green light shown in that mode. The stop aspect was generally lunar-white during darkness. All are now removed but examples can be seen on UK heritage lines. As at 2020, there are only a few remaining semaphore signals on the Western Region of Network Rail, LED signals having replaced the majority of semaphores.
Materials that were commonly used to make signal posts for semaphore signals included timber, lattice steel, tubular steel and concrete. The Southern Railway in Great Britain frequently made use of old rail for signal posts.
German semaphore home signals, which are totally different in appearance to the British semaphore signal, include one or two white arms with a red outline and a small circular disk at the end of it, and coloured lenses which display the position of the aspect(s) of the signal during nighttime operation and these arms face right of the post. German semaphore distant signals consist of one yellow disk with a black and white outline and an (optional) thin yellow arrow-shaped disk with a black and white outline. Both the disk and arrow have coloured lenses to aid drivers during nighttime. Those types were to be seen in some other countries which used German signalling principles.
British semaphores come in lower-quadrant and upper-quadrant forms. In a lower-quadrant signal, the arm pivots downwards for the less restrictive (known as "off") indication. Upper-quadrant signals, as the name implies, pivot the arm upward for "off".
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Railway semaphore signal AI simulator
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Railway semaphore signal
Railway semaphore signals are an early form of fixed railway signals. The semaphore system involves signals that 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 widely used form of mechanical signal. Designs have altered over the intervening years, and colour light signals have replaced semaphore signals in most countries, but in a few they remain in use.
The first railway semaphore signal was erected by Charles Hutton Gregory in about 1842, on the London and Croydon Railway (later the London Brighton and South Coast Railway) at New Cross, southeast London, as part of the newly enlarged layout also accommodating the South Eastern Railway. John Urpeth Rastrick claimed to have suggested the idea to Hutton Gregory.
The semaphore was swiftly embraced across Britain and North America as a fixed manual signalling system, surpassing all other types in most applications by 1870. Becoming electrically operated and automatic, accompanied by interlocking, they were widely adopted in the U.S. After 1908, with the advent of the Union Switch & Signal types "B" & "S", and the General Railway Signal Company's universal Model 2A mechanisms, manual semaphores and earlier electric disc signals quickly began to disappear.
The British semaphore signal arm consists of two parts: A wooden or metal arm (or "blade") which pivots at different angles, and a spectacle holding coloured lenses which move in front of a lamp in order to provide indications at night. Usually these were combined into a single frame, though in some types (e.g. "somersault" signals in which the arm pivoted in the centre), the arm was separate from the spectacle. The arm projects horizontally in its most restrictive aspect; other angles indicate less restrictive aspects. On double lines in Great Britain signal posts are generally placed on the left of the track and always with the semaphore arm(s) facing left with the spectacle and lamp on the right of the post or doll (but on the left of the post or doll for upper-quadrant signals). Sighting problems may mean that the post is placed on the right of the other line on double track branches and on single lines, could be placed either side of the track. North American semaphore equivalents faced right, and as generally on the European continent, on double track branches, up and down lines are opposite to those in the UK.
Depending on the arm's position, the appropriately coloured lens is illuminated from behind by either an oil lamp, a gas lamp, or an incandescent lamp run at a low voltage (white LED clusters have also been tested for this purpose). Where a green light was required, a blue lens would usually be used. When combined with the mainly yellow-emitting flame of an oil lamp, this produced a green colour; it was important that the resultant colour was not even yellow-green in appearance, as this could have been confused for a distant signal at 'caution'. Later signals using electric lamps used green lenses. Some signals converted to electric lamps from oil, used a yellow-tinted bulb with the original blue lens to maintain the correct colour or from 1996 on the Western Region of British Railways, a 12-volt 5-watt bulb was fitted but fed at 10.7 volts to produce a brilliance approximating to the colour temperature of an oil wick flame, thus providing a correct red or green aspect during darkness. Most railways in Great Britain employed lower-quadrant semaphores, where the arm dropped from the horizontal 'danger' aspect to 'clear' at up to 60° below horizontal. Variations in appearance between main and subsidiary lines or sidings also existed. On some company's lines, a three-aspect semaphore prevailed and these showed an intermediate 'Caution' aspect and thus bore a three-lensed spectacle. In 1911, the Metropolitan Line was first to use an upper-quadrant semaphore, the idea being brought over from the United States. Following nationalisation in 1948, British Railways standardised on upper-quadrant semaphores and all regions gradually adopted that mode, replacing lower-quadrant signals. However, the Western Region stayed with their well-proven lower-quadrant semaphores, with a heavy cast iron spectacle bearing circular coloured glasses eventually replacing the former thinly bordered cast spectacle frame with shaped coloured glasses. The main arms were 4 feet (1.2 m) long and subsidiaries 3 feet (0.91 m) with other subsidiaries 2 feet (0.61 m) long on these signals. Previous GWR 5-foot (1.5 m) arms placed if higher than 26 feet (7.9 m) above rail level, were changed to 4 feet (1.2 m). All replacements were of enamelled steel and bore the appropriate arm colours, red with white band for 'Stop' arm and chevroned yellow arm with black chevron for 'Distant' (Caution) arms. Both types are white on the reverse side with black band or chevron as appropriate. The final 'Call-on', Shunt' or 'Warning' arms on the Western Region were 2 feet (0.61 m) with red-white-red horizontal stripes and showed a reduced light during darkness with the appropriate black letter, C, S or W, back-lit in the 'proceed' state with a green light shown in that mode. The stop aspect was generally lunar-white during darkness. All are now removed but examples can be seen on UK heritage lines. As at 2020, there are only a few remaining semaphore signals on the Western Region of Network Rail, LED signals having replaced the majority of semaphores.
Materials that were commonly used to make signal posts for semaphore signals included timber, lattice steel, tubular steel and concrete. The Southern Railway in Great Britain frequently made use of old rail for signal posts.
German semaphore home signals, which are totally different in appearance to the British semaphore signal, include one or two white arms with a red outline and a small circular disk at the end of it, and coloured lenses which display the position of the aspect(s) of the signal during nighttime operation and these arms face right of the post. German semaphore distant signals consist of one yellow disk with a black and white outline and an (optional) thin yellow arrow-shaped disk with a black and white outline. Both the disk and arrow have coloured lenses to aid drivers during nighttime. Those types were to be seen in some other countries which used German signalling principles.
British semaphores come in lower-quadrant and upper-quadrant forms. In a lower-quadrant signal, the arm pivots downwards for the less restrictive (known as "off") indication. Upper-quadrant signals, as the name implies, pivot the arm upward for "off".