Concept
Rail transport operations are the day-to-day operations of a railway. A railway has two major components: the infrastructure (the permanent way, tracks, stations, freight facilities, viaducts, tunnels, etc.) and the rolling stock (the locomotives, passenger coaches, freight cars, etc.) Ownership and operation of these two components varies by location. In some places (notably, most of North America) private railway companies own and operate both the infrastructure and rolling stock (for example, Union Pacific). In the United Kingdom, the infrastructure is owned and maintained by Network Rail while rolling stock is largely owned and operated by private railway companies. In countries with nationalized rail systems such as China and France, both the infrastructure and rolling stock are owned and operated directly or indirectly by the national government. The operation of the railway is through a system of control, originally by mechanical means, but nowadays more usually electronic and computerized. Railway signalling Signalling systems used to control the movement of traffic may be either of fixed block or moving block variety. Fixed block signalling Most blocks are 'fixed' blocks, i.e. they delineate a section of track between two defined points. On timetable, train order, and token-based systems, blocks usually start and end at selected stations. On signalling-based systems, blocks usually start and end at signals. Alternatively, cab signalling may be in use. The lengths of blocks are designed to allow trains to operate as frequently as necessary. A lightly used branch line might have blocks many kilometres long, whilst a busy commuter railway might have blocks a few hundred metres long. Moving block signalling A disadvantage of fixed blocks is that the faster trains are permitted to run, the longer the stopping distance, and therefore the longer the blocks need to be. This decreases a line's capacity. With moving block, computers are used to calculate a 'safe zone', behind each moving train, which no other train may enter.