Railway signalling in the context of "Signalling control"

A passing loop (UK usage) or passing siding (North America) (also called a crossing loop, crossing place, refuge loop or, colloquially, a hole) is a place on a single line railway or tramway, often located at or near a station, where trains or trams travelling in opposite directions can pass each other. Trains/trams going in the same direction can also overtake, provided that the signalling arrangement allows it. A passing loop is double-ended and connected to the main track at both ends, though a dead end siding known as a refuge siding, which is much less convenient, can be used. A similar arrangement is used on the gauntlet track of cable railways and funiculars, and in passing places on single-track roads.

Ideally, the loop should be longer than all trains needing to cross at that point. Unless the loop is of sufficient length to be dynamic, the first train to arrive must stop or move very slowly, while the second to arrive may pass at speed. If one train is too long for the loop it must wait for the opposing train to enter the loop before proceeding, taking a few minutes. Ideally, the shorter train should arrive first and leave second. If both trains are too long for the loop, time-consuming "see-sawing" (or "double saw-by") operations are required for the trains to cross (see Tawa railway station).

Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas pigeon post is not. Ancient signalling systems, although sometimes quite extensive and sophisticated as in China, were generally not capable of transmitting arbitrary text messages. Possible messages were fixed and predetermined, so such systems are thus not true telegraphs.

The earliest true telegraph put into widespread use was the Chappe telegraph, an optical telegraph invented by Claude Chappe in the late 18th century. The system was used extensively in France, and European nations occupied by France, during the Napoleonic era. The electric telegraph started to replace the optical telegraph in the mid-19th century. It was first taken up in Britain in the form of the Cooke and Wheatstone telegraph, initially used mostly as an aid to railway signalling. This was quickly followed by a different system developed in the United States by Samuel Morse. The electric telegraph was slower to develop in France due to the established optical telegraph system, but an electrical telegraph was put into use with a code compatible with the Chappe optical telegraph. The Morse system was adopted as the international standard in 1865, using a modified Morse code developed in Germany in 1848.

The Liverpool and Manchester Railway (L&MR) was the first inter-city railway in the world. It opened on 15 September 1830 between the Lancashire towns of Liverpool and Manchester in England. It was also the first railway to rely exclusively on locomotives driven by steam power, with no horse-drawn traffic permitted at any time; the first to be entirely double track throughout its length; the first to have a true signalling system; the first to be fully timetabled; and the first to carry mail.

Trains were hauled by company steam locomotives between the two towns, though private wagons and carriages were allowed. Cable haulage of freight trains was down the steeply-graded 1.26-mile (2.03 km) Wapping Tunnel to Liverpool Docks from Edge Hill junction. The railway was primarily built to provide faster transport of raw materials, finished goods, and passengers between the Port of Liverpool and the cotton mills and factories of Manchester and surrounding towns.

Rail transport in Europe has diverse technological standards, operating concepts, and infrastructures. Common features are the widespread use of standard-gauge rail, high operational safety and a high proportion of electrification. Electrified railway networks in Europe operate at many different voltages, both AC and DC, varying from 750 to 25,000 volts, and signaling systems vary from country to country, complicating cross-border traffic.

The European Union (EU) aims to make cross-border operations easier as well as to introduce competition to national rail networks. EU member states were empowered to separate the provision of transport services and the management of the infrastructure by the Single European Railway Directive 2012. Usually, national railway companies were split into separate divisions or independent companies for infrastructure, passenger and freight operations. The passenger operations may be further divided into long-distance and regional services, because regional services often operate under public service obligations (which maintain services which are not economically interesting to private companies but nonetheless produce societal benefit), while long-distance services usually operate without subsidies.

The European Train Control System (ETCS) is a train protection system designed to replace the many incompatible systems used by European railways, and railways outside of Europe. ETCS is the signalling and control component of the European Rail Traffic Management System (ERTMS).