Automatic train stop


Automatic train stop or ATS is a system on a train that automatically stops a train if certain situations occur to prevent accidents. In some scenarios it functions as a type of dead man's switch. Automatic train stop differs from the concept of Automatic Train Control in that ATS usually does not feature an onboard speed control mechanism.

Overview

Mechanical systems

The invention of the fail-safe railway air brake provided an external means for stopping a train via a physical object opening a valve on the brake line to the atmosphere. Eventually known as train stops or trip stops, the first mechanical ATS system was installed in France in 1878 with some railroads in Russia following suit using a similar system in 1880. In 1901 Union Switch and Signal Company developed the first North American automatic train stop system for the Boston Elevated Railway. This system was soon adopted by the New York City Subway and other rapid transit systems in the United States.
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.
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 value 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.
While similar in operation mechanical systems around the world are generally incompatible due to the wide variety of vehicle dimensions and track gauge which will result in the mechanical stopping devices not engaging the onboard valve.

Electronic systems

Electronic systems make use of electric currents or electromagnetic fields to trigger some action in the locomotive cab. While mechanical systems were generally limited to venting the brake pipe and triggering an emergency stop, electronic systems can trigger other actions such as an acknowledgment from the driver, cutting power or a less severe application of the brakes. 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 first such electronic system was Crocodile installed on French railways starting in 1872 which used an electrified contact rail to trigger an acknowledgment from the driver. If no such acknowledgment was made in 5 seconds the train would be stopped. In the UK the Great Western Railway implemented a similar system in 1906 dubbed Automatic Train Control that served as the template for the magnetic based Automatic Warning System, which ultimately replaced it starting in the 1950s.
In the United States, the General Railway Signal corporation introduced its Intermittent Inductive Automatic Train Stop system in the 1920s which made use of inductive loops in a "shoe" mounted outside of the running rails. This system was also of the acknowledgment type and was adopted by several railroads, continuing to see service as of 2013.
In 1954, Japan introduced ATS-B, the first known variant of ATS. In 1967, ATS-S was invented, the first non-contact-based ATS to be used; in 1974, ATS-P was used for the first time, and in 1986, H-ATS was invented.

Usage around the world

United States

The majority of systems meeting the definition of Automatic Train Stop in the United States are mechanical trip stop systems associated with rapid transit lines built in the first half of the 20th century. Since 1951 ATS has been required by the Interstate Commerce Commission as a minimum safety requirement to allow passenger trains to exceed a speed limit of. The regulatory requirement refers to a system that triggers an alert in the cab of the locomotive whenever the train passes a restrictive wayside signal and that then requires the locomotive engineer to respond to the alert within a set period of time before the brakes are automatically applied.
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. Often referred to as just ATS in railroad operating books, the full name of the system is Intermittent Inductive Automatic Train Stop to differentiate it from mechanical systems being offered at the time. The popularity of ATS as a train protection mechanism fell after the introduction of track coded cab signals in the 1930s.

ATS installations in the United States

SystemOperatorLinesIn ServiceNotes
Train stopNew York City SubwayA Division 1904–presentTrips right
Train stopNew York City SubwayB Division 1915–presentTrips left
Train stopPort Authority Trans-HudsonSystem-wide1908–presentTrips left
Train stopSEPTABroad Street Subway1928–presentTrips left
Train stopSEPTAMarket–Frankford Line?-presentTrips left, at wayside signals only
Train stopMBTABlue Line1925–presentTrips both
Train stopMBTAOrange Line1901–presentTrips right, at wayside signals only
Train stopMBTARed Line1912–presentAt wayside signals only
Train stopChicago Transit AuthorityChicago 'L'?-presentTrips left
Train stopPennsylvania Railroad/Long Island Rail RoadNew York Tunnel Extension1911-?Trips right, used Hall trip valves on trains
Train stopLong Island Rail RoadDunton to Flatbush Avenue?-circa 1970Trips right, used Hall trip valves on trains.
IIATSBNSF RailwaySanta Fe Chicago to Los Angeles "Super Chief" Route1930s-presentParts of the route have had ATS removed
IIATSMetrolink and CoasterFormer ATSF San Diego Main Line.?-presentIn service milepost 179 to 249.
IIATSNew York CentralNew York to Chicago Water Level Route1920s-1971Removed by successor Penn Central
IIATSSouthern Railway2700 route miles of main line.1920s-1971Removed in favor of increased CTC use.
IIATSUnion PacificFormer Chicago & North Western North Line, Northwest Line1952–2019Used by Union Pacific on lines that also run Metra Commuter trains. Both freight and commuter locomotives must be equipped, with some exceptions.
IIATSNew Jersey TransitRiverLINE2003–presentInstalled at interlockings only. Enforces Stop.
WestcabPort Authority of Allegheny CountyPittsburgh Light Rail 42S Line from downtown to South Hills Village.1985–presentSome overlap with an Automatic Train Control system installed on the Route 47 Line.

Japan

Many trains in Japan are equipped with this system. The ATS systems in Japan are slightly similar to those used in the United States, but are mostly transponder-based. The first ATS systems in Japan were introduced in the 1920s, but did not become commonplace until the late-1960s as a result of the Mikawashima train crash which occurred in 1962.
Below is a list of ATS systems that are specific to Japan only:

JNR">Japanese National Railways">JNR/JR Group">Japan Railways Group">JR Group

In addition, various private-sector railways and subway lines have adopted their own versions of the ATS system since 1963. Like the ATS systems used by the railways in the JR Group, they are transponder-based as well, but are generally incompatible with the ATS systems used by JR.
In Wellington only a few signals at a converging junction are fitted with mechanical ATS. All electric trains are fitted.

South Korea

Some Korail and subway lines are equipped with this system.

Argentina

lines and have ATS equipped, while,, and have the more advanced Communications-based train control.

Taiwan

Many Taiwan Railways Administration trains are equipped with the Japanese ATS-SN and ATS-P systems, which serve as fallback for an ATP system introduced in 2006, of which the latter system replaced the older AWS system originally introduced in 1978 on some express trains.

United Kingdom

Some Manchester Metrolink services are ATS equipped, however this is being phased out due to the introduction of line of sight signalling.
London Underground lines are universally fitted with ATS equipment. This comprises a trip arm outside the left-hand running rail, and an air valve known as a tripcock on the leading bogie of the train. When the applicable signal shows 'danger', the trip arm is held up by a spring. If a train attempts to pass the signal, the trip arm makes contact with the tripcock. This opens the tripcock, which is connected to the train pipe of the air brakes, and causes an emergency brake application to be made. When the signal shows 'clear', the stop arm is lowered by compressed air.