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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.
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.
There are two main types of signaling aspect systems found in North America, speed signaling and weak route signaling. [citation needed] Speed signaling transmits information regarding how fast the train is permitted to be going in the upcoming segment of track; weak route signaling transmits information related to the route a train will be taking through a junction, and it is incumbent upon ...
Most rail routes have a sort of natural block layout inherent in the layout of the railway stations. This provides the ability to implement a set of blocks using manual signalling based at these locations. In this case, the station operator places a flag indicating a train has just left the station, and removes it only after a fixed time.
Some form of ATS or ATC is required on all U.S. rail lines that operate at 80 mph or more. In the 1990s, Communication-based train control (CBTC) systems started to be used in rail transit systems. These systems utilize radio communications between train and wayside equipment to perform the functions of the signaling system.
For convenience in passing it from hand to hand, the token was often in the form of a staff, typically 800 mm (31 in) long and 40 mm (1.6 in) diameter, and is referred to as a train staff. [4] Such a staff is usually literally a wooden staff with a brass plate stating the two signal boxes between which it is valid.
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.
On 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.