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ERTMS Level 4, Train Convoys or Virtual Coupling (2016)

This paper was produced by the IRSE's International Technical Committee (ITC) and published in IRSE NEWS February 2016. It was republished by the Rail Engineer magazine in May 2016.

Railways around the world are facing demands to transport more passengers and freight, but constructing new tracks is both expensive and unpopular. This leads to an ambition to run more trains on existing tracks, with challenges to the fundamental principles of present-day railway operations being proposed to achieve this goal.

One such principle is that trains following one another on the same track must be separated by a sufficient margin to ensure every train is capable of braking to a standstill before reaching the last known position of the train in front. With braking rates limited by the adhesion between steel wheel and steel rail, the required separation increases dramatically with speed — on a high speed line, trains must run several kilometres apart. The migration from fixed block to moving block signalling (e.g. CBTC or ERTMS/ETCS Level 3) is driven by an ambition to maximise capacity within this constraint, but demand for ever-increasing capacity means that the principle itself is now under challenge.

The argument for an alternative approach starts with the assertion that it is unrealistic to assume the train in front will stop instantly. Provided the two trains have similar braking rates, the trains can run much closer together. A communication link between the trains can ensure that if the leading train starts to brake, the following train will do the same and maintain separation as the two trains slow together. This concept has been described by its proponents as ‘ERTMS Level 4’, ‘Train Convoy’, or ‘Virtual Coupling’, and it features in national and international research agendas such as the UK Railway Technical Strategy and the European Shift2Rail research initiative.

Author(s):Written on behalf of the IRSE International Technical Committee (ITC) by Ian Mitchell, with contributions from Eddie Goddard, Fernando Montes, Peter Stanley, Rod Muttram, Wim Coenraad, Jacques Poré, Simon Andrews and Libor Lochman
Keywords:ERTMS; ETCS; signalling principles; virtual coupling; train convoy; convoying; capacity; headway; closer running;
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(Click to copy the Topic URL to the clipboard) Page created: 18/02/2016
Last modified: 27/11/2020
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