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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.
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.
Railway signal mast}} is a template for displaying signals on a mast for demonstration of railroad signalling aspects. It displays up to three signal heads using spotlight, one of two types of semaphore, or positional signals, along with a base and modifier plates.
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.
Behind the signal head is placed a dark backing or target, which helps improve signal visibility in bright ambient lighting. Target designs vary, but are usually round or oval, depending on the layout of the signal lamps. For each type of signal there are usually a range of target dimensions that can be chosen by the individual railroad company.
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 ...
CTC consolidates train routing decisions that were previously carried out by local signal operators or the train crews themselves. The system consists of a centralized train dispatcher's office that controls railroad interlockings and traffic flows in portions of the rail system designated as CTC territory. One hallmark of CTC is a control ...
The first reached by a train is known as the home signal. The last stop signal, known as the starting or section signal, is usually located past the points etc. and controls entry to the block section ahead. The distance between the home and starting signals is usually quite short (typically a few hundred yards), and allows a train to wait for ...