Automatic train control

Automatic train control (ATC) is a general class of train protection systems for railways that involves a speed control mechanism in response to external inputs. For example, a system could effect an emergency brake application if the driver does not react to a signal at danger. ATC systems tend to integrate various cab signalling technologies and they use more granular deceleration patterns in lieu of the rigid stops encountered with the older automatic train stop (ATS) technology. ATC can also be used with automatic train operation (ATO) and is usually considered to be the safety-critical part of a railway system. There have been numerous different safety systems referred to as "automatic train control" over time. The first experimental apparatus was installed on the Henley branch line in January 1906 by the Great Western Railway, although it would now be referred to as an automatic warning system (AWS) because the driver retained full command of braking. The term is especially common in Japan, where ATC is used on all Shinkansen (bullet train) lines, and on some conventional rail and subway lines, as a replacement for ATS.