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Railway signalling (BE), or railroad signaling (AE), is a system used to control the movement of railway traffic. Trains move on fixed rails , making them uniquely susceptible to collision . This susceptibility is exacerbated by the enormous weight and inertia of a train, which makes it difficult to quickly stop when encountering an obstacle.
Signals are most commonly mounted on trackside masts about 12 to 15 feet (3.7 to 4.6 m) high to put them in the eyeline of the engineer. Signals can also be mounted on signal bridges or cantilever masts spanning multiple tracks. Signal bridges and masts typically provide at least 20 feet (6.1 m) of clearance over the top of the rail.
Standards for North American railroad signaling in the United States are issued by the Association of American Railroads (AAR), which is a trade association of the railroads of Canada, the US, and Mexico. Their system is loosely based on practices developed in the United Kingdom during the early years of railway development. However, North ...
Railway signal in Ploiești West railway station, Romania. This type of signal is based on the German Ks signals. The signal head is the portion of a colour light signal which displays the aspects. To display a larger number of indications, a single signal might have multiple signal heads.
Signalling in the UK uses route signalling. Most railway systems around the world, however, use speed signalling. Under route signalling, the driver is informed which route has been set by an illuminated Junction Indicator mounted on the signal post. The signal will display a restrictive aspect to make the driver reduce the train's speed.
In a basic railway situation, the token can be collected personally by the driver at the start of the crew's work on a branch line, and surrendered at the end of their work there. Where the single line section is part of a through route, then it is likely that each passing train would require to surrender and collect a token at each token station.
A block instrument on the Midland Railway. Signalling block systems enable the safe and efficient operation of railways by preventing collisions between trains. The basic principle is that a track is broken up into a series of sections or "blocks".
CBTC is a signalling standard defined by the IEEE 1474 standard. [1] The original version was introduced in 1999 and updated in 2004. [1] The aim was to create consistency and standardisation between digital railway signalling systems that allow for an increase in train capacity through what the standard defines as high-resolution train location determination. [1]