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A clear block is a condition where a particular block or predetermined length of track is clear of all trains. In addition to the condition of the block ahead, The Standard Code of Operating Rules, such as those still in use on the LIRR, gives one train "superiority" over "inferior" trains.
A railway track (CwthE and UIC terminology) or railroad track (NAmE), also known as permanent way (CwthE) [1] or "P Way" (BrE [2] and Indian English), is the structure on a railway or railroad consisting of the rails, fasteners, sleepers (railroad ties in American English) and ballast (or slab track), plus the underlying subgrade.
These moving block systems have become popular since the required technology first started appearing in the 1970s. In such systems, any train on the route can listen for signals from all the other trains, and then move in a way to ensure they have enough distance to stop. Early moving block systems used a cable strung along the rail line.
Typically, the blocks are 1,000 feet (300 m) long, although some highly used lines, such as the IRT Lexington Avenue Line, use shorter blocks. Insulators divide the track segments into blocks. The two traveling rails form a track circuit, as they conduct electric current. If the track circuit is open and electricity cannot travel between the ...
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, most notably the Armagh rail disaster. This required block signalling for all passenger railways, together with interlocking, both of which form the ...
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Since every block is a fixed section of track, these systems are referred to as fixed block systems. In a moving block CBTC system the protected section for each train is a "block" that moves with and trails behind it, and provides continuous communication of the train's exact position via radio, inductive loop, etc. [8]
For example, on a flat stretch of high speed track, a block can be a full 1500 metres long, while in the terminal areas of the Channel Tunnel, blocks are one-tenth as long. Network Code, a number which determines the interpretation of the speed codes which should be taken by the train's computer. For example, on high speed lines where the ...