Cab Signalling - Overview

Overview

The main purpose of a signal system is to enforce a safe separation between trains and to enforce speed limits. The cab signal system is an improvement over the wayside signal system, where visual signals beside or above the right-of-way govern the movement of trains, without any means of enforcing the signal automatically. While early cab signal systems only repeat the wayside signal aspect displayed, all modern systems have an enforcement component which can automatically stop a train.

The first such systems were installed on an experimental basis in the 1910s in the United Kingdom, 1920s in the United States, and later in the Netherlands in the 1940s. High-speed trains such as those in Japan, Northeastern United States, Britain, France, and Germany use such systems in principle, though they are mutually incompatible.

The European Rail Traffic Management System (ERTMS) is a multi-national standard that is progressively being developed in Europe, with an aim to improve interoperability. The train-control component of ERTMS, termed European Train Control System (ETCS), is a functional specification that incorporates the former national standards of several European countries. The German Indusi, German LZB, British TPWS, and the French TVM could all be made ETCS-compliant with modifications.

In North America, the power-frequency coded track circuit system developed by the Pennsylvania Railroad (PRR) and Union Switch & Signal (US&S) is the de facto standard in the Northeast. Variations of this system are also in use on many rapid transit systems, including the MBTA Red Line, London Underground Victoria Line, and form the basis for the first generation Shinkansen signalling developed by Japan National Railways (JNR).