Railway infrastructure manager
A railway infrastructure manager is a rail transport company or body of other type, responsible for maintaining railway infrastructure. The European Union defines it as "any body or undertaking that is responsible in particular for establishing and maintaining railway infrastructure. This may also include the management of infrastructure control and safety systems. The functions of the infrastructure manager on a network or part of a network may be allocated to different bodies or undertakings" This includes mainly railway track and catenary, if the railway line is electrified, and respective command and control systems. It can also include the stations and power supply network. A significant proportion of these companies are state-owned monopolies, responsible for all or most of the railway infrastructure within a given country.
Ownership and operation of these two components varies by location. In some places private railway companies own and operate both the infrastructure and rolling stock. 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, both the infrastructure and rolling stock are owned and operated directly or indirectly by the national government. In the European Union, separation of infrastructure and operation is mandated by law, so train operation is performed by another type of company, a railway undertaking which must be provided with non-discriminatory access to any railway path within the EU. Outside the European Union it is possible that the same company is owning the infrastructure and also operating trains and in that case this designation might not make sense. Infrastructure managers charge for the use of its network.
Management of railway infrastructure
Operation
The operation of the railway is through a system of control, originally by mechanical means, but nowadays more usually electronic and computerized.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. The system depends on precise knowledge of where each train is and how fast it is moving. With moving block, lineside signals are not provided, and instructions are passed direct to the trains. It has the advantage of increasing track capacity by allowing trains to run much closer together. The system is only used on very few independent networks such as underground lines.