Automatic train stop

[citation needed] In 1901 Union Switch and Signal Company developed the first North American automatic train stop system for the Boston Elevated Railway.

[1] Mechanical ATS was more popular on rapid transit systems and dedicated commuter rail than freight or long-distance passenger lines due to a combination of the increased complexity found in mainline railroad operations, the risk of inadvertent activation by debris or other wayside appliances, and the danger of emergency brake applications at high speeds.

Moreover, the forces involved in a physical tripping action can begin to damage both the wayside and vehicle borne equipment at speeds over 70 miles per hour (110 km/h).

In 1910 the Pennsylvania and Long Island Rail Roads installed a mechanical ATS system covering various lines to New York Penn Station using the patented Hall trip valve which was designed to prevent inadvertent activations from debris, however the system was only installed on locomotives and multiple units traveling to Penn Station and did not see further adoption.

Without physical contact electronic systems could be used with higher speeds, limited only by the equipment's ability to sense the signal from stop devices.

The most popular implementation of ATS for the mainline railroad industry was made by the General Railway Signal company starting in the 1920s and consisted of inductive coils mounted just outside the right hand rail in relation to the direction of travel.

The first ATS system in South Korea was installed on the Korail network in 1969, followed by Seoul Subway Line 1 in 1974 (similar to Japanese ATS-S).

Some of the Firema T-68 and Bombardier M5000 trams of the Manchester Metrolink trains were equipped with ATS, however this is gradually being phased out due to the introduction of line of sight signalling.

This comprises a trip arm just outside the right-hand running rail, and an air valve known as a tripcock on the leading bogie of the train.