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Automatic train stop
Automatic train stop
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Automatic train stop or ATS is a system on a train that automatically stops a train if certain situations occur (unresponsive train operator, earthquake, disconnected rail, train running over a stop signal, etc.) 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

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Mechanical systems

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Preserved mechanically-operated ATS system formerly used on Tokyo Metro Ginza Line (installed 1927–1941, replaced with CS-ATC and TASC in 1993)

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.[citation needed] 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.[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.

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

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ATS pickup on the leading truck of a San Diego Coaster F40PH

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 (train protection system) 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.[2]

In 1954, Japan introduced ATS-B, the first known variant of ATS. In 1967, ATS-S (and its various supplements) 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.[3][better source needed]

Usage around the world

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United States

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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 (later the Federal Railroad Administration) as a minimum safety requirement to allow passenger trains to exceed a speed limit of 79 mph (127 km/h). 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

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System Operator Lines In Service Notes
Train stop New York City Subway A Division (IRT) 1904–present Trips right
B Division (BMT and IND) 1915–present Trips left
Port Authority Trans-Hudson System-wide 1908–present Trips left
SEPTA Broad Street Subway 1928–present Trips left
Market–Frankford Line ?-present Trips left, at wayside signals only
MBTA Blue Line 1925–present Trips both
Orange Line 1901–present Trips right, at wayside signals only
Red Line 1912–present At wayside signals only
Chicago Transit Authority Chicago 'L' ?-present Trips left, at wayside signals only
Pennsylvania Railroad/Long Island Rail Road New York Tunnel Extension 1911-? Trips right, used Hall trip valves on trains
Long Island Rail Road Dunton to Flatbush Avenue[4] ?-circa 1970 Trips right, used Hall trip valves on trains.
IIATS BNSF Railway Santa Fe Chicago to Los Angeles "Super Chief" Route 1930s-present Parts of the route have had ATS removed
Metrolink and Coaster Former ATSF San Diego Main Line. ?-present In service milepost 179 to 249.
New York Central New York to Chicago Water Level Route 1920s-1971 Removed by successor Penn Central
Southern Railway 2700 route miles of main line. 1920s-1971 Removed in favor of increased CTC use.
Union Pacific Former Chicago & North Western North Line, Northwest Line 1952–2019 Used by Union Pacific on lines that also run Metra Commuter trains. Both freight and commuter locomotives must be equipped, with some exceptions.
New Jersey Transit RiverLINE 2003–present Installed at interlockings only. Enforces Stop.
Westcab Port Authority of Allegheny County Pittsburgh Light Rail 42S Line from downtown to South Hills Village. 1985–present Some overlap with an Automatic Train Control system installed on the Route 47 Line.

Japan

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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 nowadays primarily transponder-based. The first mechanical ATS systems in Japan were introduced on the Tōkaidō Main Line in 1921, followed by the Tokyo Metro Ginza Line in 1927; but ATS did not become commonplace in the country 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:

  • ATS-B (also supplemented with S-type transponder; now obsolete since 2009)
  • ATS-Dx (ATS using D-type transponder; always supplemented with: ATS-DF (JR Freight), ATS-DK (JR Kyushu) or ATS-DN (JR Hokkaido))
  • ATS-S(x) (ATS using S-type transponder; always supplemented with: ATS-SF (JR Freight), ATS-SK (JR Kyushu), ATS-SM (Mizushima Rinkai Railway), ATS-SN (JR East and JR Hokkaido), ATS-SS (JR Shikoku), ATS-ST (JR Central) or ATS-SW (JR West), the last two letters corresponding to the type of transponder used with the S-type transponder)
  • ATS-P (ATS using pattern renewal transponder; variants are ATS-PF (JR Freight), ATS-PN (Low-cost introduction type), ATS-PT (JR Central) and ATS-Ps (Frequency change cab signalling Type; used for e.g. on Senseki Line and Sendai Airport Line, and on operational steam trains))[5]
  • D-TAS (introduced by JR West in 2012; previously called ATS-M and ATS-DW during development)
  • H-ATS (formerly used on the EF66 locomotive)
Meitetsu ATS transponders near a buffer stop at Saya Station. This transponder arrangement is similar in principle to "Moorgate control" used on the London Underground.
ATS pickups (yellow circles) on a Hankyu 3000 series train.

In addition, various private-sector railways and subway lines have adopted their own versions of the ATS system since the 1960s. 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.

New Zealand

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In Wellington only a few signals at a converging junction are fitted with mechanical ATS. All electric trains are fitted.

South Korea

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Some Korail and subway lines are equipped with this system, as follows: Line 1, Line 4 (above ground section between Geumjeong and Oido stations), Suin-Bundang Line (between Gosaek and Incheon), Gyeongui-Jungang Line, and the Gyeongchun Line. 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).

Argentina

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Buenos Aires Underground lines and have ATS equipped, while , , and have the more advanced Communications-based train control.[6]

The Roca Line is ATS equipped in its electrified branches since 1985.[7] Its ATS was provided by Japanese company Nippon Signal.[8][7]

Taiwan

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Many Taiwan Railways Administration trains are equipped with an Ericsson-developed ATS system since the late-1970s (similar to Japanese ATS-SN and ATS-P),[9] which serve as fallback for a Bombardier-designed ATP system introduced in 2006 (equivalent to ETCS Level 1), of which the latter system replaced the older AWS system originally introduced in 1978 on the EMU100 and EMU200 express trains.

United Kingdom

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The Manchester Metrolink uses ATS equipment between Timperley and Altrincham Interchange. This consists of electromagnetic beacons before the applicable signal. If a signal is passed at danger, the ATS device inside the tram will apply the track brakes. [10] This system used to be universal along the system, but has been narrowed down to just this section because of recent resignalling to the system.

An ATS beacon before a signal
Retrofitted ATS device from an older vehicle
Factory-fitted ATS device

London Underground lines are universally fitted with ATS equipment. 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. 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.

China

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Many China Railway trunk lines use an ATS system introduced in the late-1980s, similar in principle to Japanese ATS-P and ATC.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia
from Grokipedia
Automatic Train Stop (ATS) is a system designed to automatically apply a train's emergency brakes if it passes a signal at danger without authorization, thereby preventing collisions and enforcing signal compliance to mitigate . The origins of ATS trace back to the late 19th century. The earliest system was the French "" in 1872, followed by the first U.S. experimental installation occurring in 1876 on the Pennsylvania Railroad's Middle Division, where a trackside trip device broke a glass tube in the train's air line to trigger the brakes. The first permanent implementation came in 1901 on the Elevated Railway, utilizing mechanical wayside trips that directly engaged the train's brake valve to enforce stops at restrictive signals. Early systems were rudimentary mechanical devices, and evolved in the early to include intermittent inductive mechanisms, where onboard receivers detect wayside beacons or inductors linked to signals, applying brakes only if the signal aspect requires a stop. ATS systems are typically intermittent, activating only at specific points such as signals or speed restrictions, and achieve safety integrity levels like SIL2 through embedded sensors and braking interfaces without requiring continuous train localization. They form a foundational component of broader train protection frameworks, including (ATC) and Automatic Train Protection (ATP), which integrate speed supervision and collision avoidance, and have influenced modern implementations like (PTC) in . Primarily deployed in urban and mainline railroads, particularly in the United States and , ATS enhances operational by providing audible warnings and automatic enforcement, with applications extending to speed control on curves or viaducts via specialized magnets.

History

Early mechanical systems

The earliest mechanical automatic train stop (ATS) systems were developed in the late to address growing safety concerns from rising train speeds and signaling errors. One of the first trials took place in on the Pennsylvania Railroad's Middle Division, where a track trip device physically broke a in the train's air brake line upon encountering a stop signal, triggering an automatic brake application. The first permanent installation of a mechanical ATS occurred in 1903 on the Boston Elevated Railway, marking a significant advancement in urban rail safety. This system employed wayside trip mechanisms that directly engaged brake valves on passing trains, ensuring automatic halting if a restrictive signal was ignored. By 1904, the newly opened Interborough Rapid Transit (IRT) subway in integrated similar mechanical train stops into its comprehensive signaling infrastructure, designed by the Company. These featured rigid trip arms positioned at signal locations; if a train passed a red signal without acknowledgment, the arm struck a on the undercarriage, venting from the brake pipe and applying emergency brakes within seconds. At their core, these early mechanical ATS designs relied on physical interactions between trackside elements—such as ramps, arms, or trips—and onboard levers connected to the system. When a train approached a stop signal, the wayside device remained raised to engage the train's mechanism, forcing a application unless manually forestalled by the operator. This approach provided a simple, enforcement of signal indications, preventing rear-end collisions in block sections by overriding . European railways also explored mechanical ATS during this period, with the conducting trials of a mechanical in 1915 to test automatic brake enforcement at signals. However, these foundational designs faced notable limitations that curtailed their widespread adoption. Their reliance on direct physical contact made them prone to high maintenance demands, as exposed components suffered from wear, weather exposure, and debris accumulation, requiring frequent inspections and adjustments. Additionally, the systems were ineffective at higher speeds—typically above 30-40 mph—due to the quadratic increase in forces needed for reliable engagement, restricting their use primarily to low-speed urban or yard operations. Mechanical failures posed accident risks, as seen in several 1920s U.S. subway incidents where trip mechanisms malfunctioned, allowing signal violations and contributing to derailments or collisions. These mechanical systems established essential principles for train protection but highlighted the need for more robust solutions, paving the way for the transition to electronic technologies in subsequent decades.

Transition to electronic systems

The transition from mechanical to electronic automatic train stop (ATS) systems in the mid-20th century addressed the reliability issues of early physical mechanisms, such as trip arms that could fail due to , wear, or misalignment, by leveraging electromagnetic principles for non-contact . These electronic innovations enabled intermittent checks of train speed and signal compliance without continuous power consumption, improving on high-speed lines while reducing needs. Key to this shift were devices like inductive loops or track magnets that energized onboard circuits, triggering relays to sound alarms or apply brakes if the driver ignored a restrictive signal. The earliest electronic ATS system was the French Crocodile, developed on the in , which used an electrified rail contact to relay signal changes directly to the cab, alerting the driver to proceed or stop. Practical enhancements with electromagnetic track contacts in the allowed for more robust operation across electrified networks, marking the system's into a viable alternative to mechanical methods. In the United States, the Intermittent Inductive Automatic Train Stop (IIATS), introduced by the General Railway Signal Company, represented a major advancement; its first trial occurred in 1919 on the Buffalo, Rochester & Pittsburgh Railway, employing magnetic induction from wayside inductors to convey coded signals to the train. The implemented IIATS in 1925 on select routes, integrating it with track circuits to enforce speed restrictions and automatic braking via onboard relays. This system gained momentum following a 1922 mandate requiring ATS on passenger trains exceeding 79 mph (127 km/h) to prevent accidents. In the , the Automatic Warning System (AWS) was approved by the Ministry of Transport in November 1956 as a cost-effective electronic solution, utilizing permanent magnets and electro-mechanical inductors placed before signals to deliver audible warnings—a bell for clear aspects or a horn for cautions—followed by automatic brake application if unacknowledged. AWS's magnet-based design allowed selective enforcement without full continuous control, facilitating rapid rollout on British Railways. pioneered its electronic ATS variant with ATS-B in 1954, a basic system that used trackside beacons to transmit speed and stop commands to onboard receivers, responding to post-war safety demands after multiple signal-passed-at-danger incidents. Adoption accelerated after the 1962 Mikawashima crash on the Joban Line, where a freight train's signal violation caused a collision killing 160 people and injuring 296, underscoring the need for reliable electronic overrides. These early electronic systems shared core concepts, including inductive or magnetic transmission of signal data from trackside to trainborne antennas, and for driver alerts or braking, which proved more adaptable than mechanical predecessors for expanding rail networks up to the .

Modern integrations and developments

In the of automatic train stop (ATS) systems, a significant shift has occurred toward continuous supervision models integrated within automatic train protection (ATP) frameworks, contrasting with earlier intermittent approaches that relied on periodic trackside acknowledgments. This transition enhances real-time monitoring and enforcement, reducing in high-risk scenarios. In the United States, (PTC), mandated by the Rail Safety Improvement Act of 2008, exemplifies this integration, requiring railroads to implement systems capable of automatically stopping trains to prevent collisions, derailments, and incursions into work zones by December 31, 2015. ATS functions as a core component of PTC, enforcing speed restrictions and halting trains upon signal violations. The implementation of PTC faced delays due to technical and infrastructural challenges, leading to a key event in 2015 when the Positive Train Control Enforcement and Implementation Act extended the deadline to December 31, 2018, with full operational deployment achieved across mandated lines by 2020. In , the (ETCS), developed from the 1990s onward, represents another milestone in continuous ATS integration. ETCS Level 1 employs balise-based intermittent positioning for automatic stop enforcement at fixed points, while Level 2 advances to continuous radio communication for dynamic speed supervision and braking intervention, achieving widespread adoption across EU rail networks by the . In , the indigenous KAVACH system, developed by the starting in 2018, incorporates ATS features within an ATP framework to prevent collisions through automatic braking and speed control. Field trials commenced in 2022, with initial rollout on 1,465 route kilometers in the South Central Railway by 2023, and expansion targeted through 2025 amid a nationwide safety mandate following the June 2023 train accident, which prompted accelerated deployment to cover over 2,000 kilometers annually. This system enforces automatic stops for and over-speeding, enhancing collision avoidance on dense corridors. Recent developments include exploratory pilots for AI-enhanced detection in predictive stopping, such as those under the EU's AI4RAILs initiative in 2024, which integrate for anticipatory braking based on real-time . The global rail automation market, encompassing ATS advancements, is projected to grow at a (CAGR) of approximately 7.1% from 2025 to 2035, driven by demand for integrated safety technologies in emerging networks.

Principles of Operation

Mechanical ATS mechanisms

Mechanical automatic train stop (ATS) systems rely on physical interactions between trackside elements and onboard components to enforce signal indications and prevent collisions by automatically applying the train's brakes. At restrictive stop signals, a trackside trip arm or ramp, positioned adjacent to the rail at a specified height (typically 2.5 to 3 inches above the rail top), is raised into the path of the train's contact element, often a lever or shoe mounted on the locomotive at a matching height and lateral distance from the rail. As the train approaches, if the signal remains at stop, the raised arm engages the lever, mechanically actuating a valve that vents the brake pipe, initiating a full service brake application throughout the train. This process ensures the train stops within the calculated stopping distance from the signal, with the brake application commencing no later than 8 seconds after engagement to match manual service rates. The interaction between the ramp and is a straightforward mechanical linkage: the ramp's upward protrusion strikes the , which pivots to open an exhaust port in the brake system, rapidly reducing brake pipe and engaging the on all cars. For permissive signals allowing movement, the trip arm is lowered out of the way, permitting the to pass without activation; however, manual override is limited to a forestalling device on the , which the can use to acknowledge the indication and prevent brake application, but only within a brief (such as 30 seconds) and solely at non-stop signals. After activation at a stop signal, the cannot be released until the resets the system manually, confirming the signal has cleared, thus preventing premature resumption of movement. Safety features in mechanical ATS include redundant springs on both the trackside arm and onboard lever to ensure reliable return to position after engagement, maintaining operative alignment under varying conditions like or minor impacts. These systems enforce predetermined speed limits, typically up to 79 mph for standard operation, with automatic application if exceeded, and reduced to restricted speeds of 20 mph or less if the device fails en route to mitigate risks. The design prioritizes operation, where any interruption in the normal state defaults to application, enhancing reliability in low- to medium-speed rail environments. Common failure modes arise from mechanical wear on pivoting parts like the joints or arm hinges, leading to incomplete engagement; misalignment caused by track vibrations or settlement, which can position the arm outside the ; and general incompatibility with high-speed operations above 80 mph, where dynamic forces exacerbate these issues and increase stopping distance variability. Regular , including monthly gauging of heights and alignments and semi-annual functional tests, is required to detect and correct such faults, ensuring the system's integrity.

Electronic ATS technologies

Electronic Automatic Train Stop (ATS) systems utilize and radio-frequency technologies to transmit safety-critical information from trackside to onboard equipment, enabling automated enforcement of speed limits and signal aspects without physical contact. These systems replace mechanical tripping mechanisms with coded electrical signals, allowing for precise detection of hazardous conditions such as passing a danger signal. Inductive technologies, such as those employed in intermittent inductive ATS (IIATS), involve wayside s placed near signals that interact with an onboard pickup coil to generate voltage s when passes. In IIATS, the wayside inductor remains unshorted for restrictive aspects, inducing a voltage change that triggers an alarm if unacknowledged, leading to automatic brake application via de-energization. Coded track circuits integrated with inductive systems use frequencies like 75 Hz and 120 Hz to enforce speed restrictions, where the onboard receiver decodes the pulse rate to verify compliance with signal indications. Transponder-based systems, akin to RFID tags or balises, provide location-specific transmission. For instance, the Japanese ATS-P employs transponders for bi-directional communication, relaying signal aspects and to the next stop signal to an onboard computer, which generates a braking pattern tailored to the train's characteristics. If the train's speed exceeds this pattern—indicating an invalid condition such as or passing a danger signal—the system automatically applies maximum braking power without driver intervention. Operational variations distinguish intermittent systems, which perform spot checks at key points like signals using short-range pulses, from continuous systems that employ looped inductive circuits for ongoing monitoring, as seen in ATP setups like TVM where speed codes (0-300 km/h) are transmitted via track circuits. In both, onboard antennas or coils detect trackside pulses within a range of 100-200 meters, with response times under 2 seconds to minimize collision risk; coding schemes, such as polarity reversal in inductors, reduce false positives by ensuring signals are only activated for genuine hazards. A prominent example is the UK's Automatic Warning System (AWS), which uses electro-permanent positioned approximately 185 meters before signals: a permanent induces a cautionary horn and potential brake warning, while an energized (north pole up) for clear aspects cancels this with a bell and visual acknowledgment. If the driver fails to acknowledge a caution, relays cut power and apply , enforcing the stop with a detection speed up to 100 mph and response latency around 1 second.

Integration with broader train protection systems

Automatic Train Stop (ATS) functions as a critical subsystem within broader Automatic Train Protection (ATP) frameworks, primarily enforcing emergency stops to prevent collisions or signal violations while integrating with detection and enforcement. In systems like the (ETCS) Level 1, ATS-like mechanisms rely on fixed transponders placed along the track to transmit position-specific braking commands, ensuring trains adhere to movement authorities without continuous radio-based supervision. This intermittent approach overlays ATP onto existing signaling infrastructure, providing vital against unauthorized movements at low cost. Integration with (ATC) enhances ATS by combining speed supervision with enforced braking, allowing for safer operations on dense networks. In Japanese railways, ATC and ATS have been paired since the 1960s, with ATC delivering continuous velocity monitoring on high-speed lines and ATS activating automatic halts on conventional routes in response to restrictive signals. This synergy, evolved from post-1962 safety reforms, supports reliable service with minimal delays, as ATC patterns adjust dynamically while ATS serves as the for driver oversight. In (CBTC) environments, particularly for Grades of Automation (GoA) reaching GoA4 in fully unattended metros, ATS provides essential fallback protection during system disruptions, enabling remote stop commands or reversion to conventional detection methods like track circuits. This layered design ensures operational continuity, with ATS enforcing emergency interventions if primary ATP or (ATO) fails. Such enhancements allow seamless progression to driverless modes while maintaining redundancy. These integrations yield substantial safety gains, reducing Signals Passed at Danger (SPAD) incidents by 70-90% in equipped corridors according to operational analyses, and rendering ATS mandatory in to mitigate collision risks. For example, similar systems like the UK's Train Protection and Warning System (TPWS) have achieved over 90% SPAD reductions since implementation. Nonetheless, interoperability challenges persist, especially in retrofitting legacy ATS into modern setups like the US (PTC), where diverse vendor protocols and shared network requirements complicate cross-railroad compatibility and delay full deployment.

Components and Functionality

Trackside infrastructure

Trackside infrastructure for ATS includes wayside devices like trip arms, inductors, and balises positioned at signals and restriction points to interface with onboard systems, ensuring enforcement of speed and stop requirements.

Mechanical Components

Trackside mechanical elements in automatic train stop (ATS) systems primarily consist of trip stops or arms positioned at signals to enforce stops by engaging onboard levers if a train passes a restrictive indication. These devices are typically constructed from durable to withstand environmental exposure and repeated mechanical contact. Trip arms are raised to engage the train's undercarriage trip cock when in the stop position, with precise alignment from the rail gage side to ensure reliable actuation without false triggers.

Electronic Components

Electronic trackside infrastructure for ATS includes inductive coils and electromagnets designed for intermittent activation at key points, such as near signals. In North American systems, intermittent inductive ATS employs buried or surface-mounted roadway inductors that transmit coded signals to onboard receivers, with insulation maintained to prevent signal degradation. In European contexts, such as the Automatic Warning System (AWS), 25 Hz electromagnets are used alongside permanent magnets, placed on the track centerline to induce warnings or stops based on signal aspects. Balises, or active/passive transponders in ETCS-compatible ATS integrations, are fixed to sleepers or embedded in the track, transmitting data telegrams of variable length at low power; they are placed at strategic intervals corresponding to signaling and movement authority points.

Installation Practices

Installation of trackside ATS elements requires precise alignment with signaling locations to synchronize with block boundaries and stopping distances. Mechanical trip arms are mounted on signal masts or dedicated stands, positioned at least one stopping distance before the signal they protect, with low-voltage DC power supplies (often 24 V) for any motorized raising/lowering mechanisms to ensure fail-safe operation. Electronic components, like inductive coils, are buried or surface-mounted with insulated joints to isolate circuits, using separate or isolated power sources to prevent failures from mainline interruptions. Balises are installed in groups of up to four, with a maximum intra-group spacing of 12 meters, secured against vibration and weather using corrosion-resistant housings compliant with EN 50155 standards. All elements must operate under varying speeds, weather, and wear conditions without degradation.

Maintenance Requirements

Routine maintenance focuses on preserving functionality and preventing , with annual inspections mandated for key circuits and components. Trackside elements, excluding track circuits, undergo monthly visual and dimensional gaging for alignment, height, and , followed by semi-annual functional tests to verify initiation at stopping distances. Inductive coils and magnets are checked for insulation integrity and electromagnetic output, with faulty units taken out of service by setting signals to restrictive aspects until repaired. inspections target constructions and buried elements, using non-destructive methods to detect degradation from moisture or abrasion, ensuring compliance with principles. Acknowledgment and cut-in circuits receive annual testing to confirm reliable activation.

Standards and Regulatory Framework

In the United States, the (FRA) requires the installation of an automatic cab signal, automatic train stop (ATS), or (ATC) system on lines where passenger trains operate at speeds of 80 mph or more, integrated with block-signal systems for automatic brake application. For freight operations, similar requirements apply under (PTC) on specified high-risk lines. Systems must de-energize track circuits with a 0.06-ohm shunt and prohibit strap-iron inductors on tracks allowing over 20 mph. European standards for ETCS balises specify low-voltage DC operation (up to 15 V), with trackside equipment tested to SIL4 safety levels and positioned to avoid metal mass interference within 1.5 meters. Globally, installations prioritize , with electronic upgrades costing approximately $50,000 to $200,000 per mile depending on and existing (as of 2018). These trackside elements complement onboard systems by providing fixed enforcement points, ensuring trains halt automatically upon signal violations.

Onboard detection and response systems

Onboard detection systems in Automatic Train Stop (ATS) setups primarily rely on vehicle-mounted hardware to receive signals from trackside elements, ensuring the train can identify speed restrictions or stop commands. In mechanical implementations, such as those in the , detection occurs via a contact shoe or lever positioned on the undercarriage of the train car, which physically engages with raised trackside trip arms activated by restrictive signals. These mechanical detectors trigger an immediate response without electronic processing, providing a simple mechanism for urban rail environments. For electronic ATS variants, including those integrated into (PTC), detection uses inductive pickup coils mounted near the front of the lead car, typically positioned inches above the rails to capture coded signals. Additionally, transponder readers on the interface with wayside tags, such as in Amtrak's ACSES system, where the onboard unit decodes position and authority data as the train passes over the devices. Response mechanisms in onboard ATS systems interface directly with the train's braking and controls to enforce limits. Upon detecting a violation, such as passing a restrictive signal, interface relays activate to cut power to the traction motors and apply emergency brakes, achieving deceleration rates of approximately 1.0 to 1.5 m/s² (0.1 to 0.15 g) depending on the rail system's design and load conditions. These relays, often electromechanical, ensure rapid enforcement by overriding manual controls, while audible alarms and visual indicators in the cab alert the operator to acknowledge or intervene before full braking engages. In PTC-equipped locomotives, the onboard computer processes detection inputs to modulate responses, potentially incorporating GPS for precise positioning to prevent or incursions. Power for onboard ATS components is drawn from the train's battery , typically operating at 24 to 110 V DC to support reliable detection and functions across various classes. designs are integral, with spring-applied brakes that default to the engaged position upon power loss or failure, ensuring automatic stopping without reliance on continuous electrical supply. This configuration aligns with railway safety standards, where loss of vital power triggers emergency procedures independently of trackside inputs. Routine testing maintains onboard ATS integrity, including daily acknowledgment procedures at maintenance depots where operators verify system functionality through simulated signal responses and checks. Diagnostics are handled via the onboard unit, which logs faults and supports self-tests to confirm coil integrity, readability, and operation before . Representative examples illustrate the evolution of these systems: the Subway's mechanical ATS employs undercarriage levers for direct trip arm detection, a low-tech approach still in use on legacy lines for immediate emergency stops. In contrast, modern PTC implementations on U.S. freight and passenger locomotives augment inductive coils and readers with GPS receivers, enabling continuous monitoring and precise enforcement of movement authorities.

Signal interaction and override procedures

Automatic Train Stop (ATS) systems interface with signaling by activating primarily in response to restrictive signal aspects, such as a or stop indication, to enforce safe braking. , ATS initiates an automatic brake application at least the calculated stopping distance from the entrance to a block occupied by a or displaying a restrictive condition, ensuring the train halts before reaching the . Similarly, in Japanese ATS implementations like ATS-S, the system detects a stop signal via track circuits and wayside inductors, transmitting a warning when the train approaches within detection range, typically aligned with signal aspects to prevent passing restrictive indications without intervention. Override procedures in ATS allow limited temporary suppression of the system for operational needs, such as shunting movements, often through a cab-mounted cut-out switch or forestalling device that delays brake application. In U.S. systems, the forestalling mechanism permits the operator to acknowledge and momentarily, but the brakes cannot be released until the restrictive condition clears or the system is manually reset after a . Japanese ATS variants, such as ATS-P, incorporate transponders for aspect confirmation but require full system reset post-, with cut-out options restricted to scenarios under strict protocols. Operational procedures mandate acknowledgment of ATS warnings to avoid penalty . Upon detecting a restrictive aspect, an audible alarm sounds in the cab—such as a bell in Japanese ATS-S—requiring the operator to confirm by shifting the and pressing a within a specified timeframe, typically 5 seconds in or up to 30 seconds in U.S. intermittent inductive ATS. Failure to acknowledge triggers a penalty application: a full service in U.S. systems, independent of the brake valve position, or emergency braking in Japanese setups, bringing the train to a complete stop. Safety protocols in ATS prohibit overrides on absolute stop indications to prevent incidents, ensuring automatic enforcement at critical points. Systems log activation events, acknowledgments, and brake applications via onboard recorders or data for post-incident investigations, maintaining a tamper-proof . In cases of system failure, operations revert to restricted speeds (e.g., 40 mph in the U.S.) without allowance for full overrides. Regulations governing ATS emphasize rigorous testing and compliance. In the United States, rules under 49 CFR Part 236 Subpart E require daily acknowledgment tests, periodic full-system checks every 92 days, and monthly roadway inspections to verify inductor functionality and response. In , following the 1962 Mikawashima accident, (JNR) introduced ATS protocols mandating installation on principal lines by 1966, with the Ministry of Transport enforcing speed-check integrations by 1967 to enhance signal interaction reliability.

Global Implementations

North America

In the United States, the (FRA) has mandated automatic train stop (ATS) systems for passenger trains operating above 79 miles per hour since a 1947 order, which established speed limits without such protections to enhance safety on non-signaled tracks. This requirement evolved into modern standards under FRA regulations, requiring intermittent inductive ATS (IIATS) on freight lines for speeds exceeding certain thresholds, with implementations dating back to the 1920s and 1930s on major carriers like the Atchison, Topeka and Santa Fe Railway (predecessor to BNSF) and Union Pacific. IIATS uses wayside inductors to enforce signal compliance by automatically applying brakes if a restrictive aspect is ignored, remaining in use on select freight routes despite ongoing transitions. The Rail Safety Improvement Act of 2008 (RSIA) further advanced ATS through the mandate for Positive Train Control (PTC), a comprehensive system incorporating automatic stop functionality to prevent collisions and overspeed events. PTC deployment, required on approximately 60,000 miles of track including high-hazard freight and intercity passenger routes, reached full operational status by the extended deadline of December 31, 2020, covering key networks operated by Class I railroads such as BNSF and Union Pacific. This integration provides enforced stopping at signal violations and temporary speed restrictions, directly addressing derailment risks from human error. In Canada, (TC) enforces similar regulatory frameworks for (ATC) and ATS under the Railway Safety Act, aligning closely with U.S. standards to ensure cross-border compatibility on shared corridors. systems are deployed on VIA Rail's high-density Quebec-Windsor corridor, utilizing continuous supervision to maintain speed limits and signal adherence, while legacy mechanical ATS persists on urban networks like the Toronto Transit Commission's subway Line 1, where trip stops physically enforce stops at red signals. TC's ongoing Enhanced Train Control initiative builds on these foundations, prioritizing automatic protection on passenger routes. ATS coverage in achieves near-universal application on high-speed passenger operations, with 100% of relevant U.S. intercity routes equipped via PTC or legacy systems, while freight coverage remains partial, focusing on hazardous material lines and high-traffic mainlines under FRA mandates. Recent FRA audits in 2023 confirmed 99% compliance across mandated railroads, highlighting PTC's role in averting potential derailments through real-time enforcement.

Asia

In Asia, automatic train stop (ATS) systems have evolved to address the challenges of high-density rail networks, incorporating continuous monitoring and rapid response mechanisms tailored to urban congestion and high-speed operations. These adaptations emphasize integration with local signaling traditions while enhancing safety in regions with massive passenger volumes, such as Japan's lines and China's extensive high-speed corridors. Japan's ATS implementations originated from the need to prevent signal-passed-at-danger incidents following the 1962 Mikawashima crash, which killed 160 people due to error, prompting the nationwide rollout of ATS-S by 1966 across (JNR) lines. This mechanical system used track circuits to enforce braking if s ignored stop signals for over five seconds. In the , JNR developed ATS-P to account for varying braking profiles, transmitting distance-to-stop data via transponders and enabling automatic braking without acknowledgment; it was tested in 1980 on the Kansai Line and later expanded to urban routes. JR East's ATS-SN variant, introduced as an enhancement to ATS-S, added speed verification coils at signals to trigger emergency brakes, covering key conventional lines since the late . On the network, (ATC) evolved post-1964 Tokaido launch to support speeds over 200 km/h, providing continuous cab signaling and full coverage across all lines for collision prevention. China's Chinese Train Control System (CTCS) incorporates ATS functionalities through levels 0 and 1, which build on legacy cab signaling introduced in the to supervise speeds up to 160 km/h on conventional lines. CTCS-0 relies on trackside balises for intermittent data transmission to onboard units, enforcing automatic stops for signal violations and integrating with Eurobalise readers for enhanced precision. As of late , these systems support operations across China's national railway network of over 150,000 km, including approximately 50,000 km of high-speed lines, ensuring near-universal coverage on urban and express routes. In , the indigenous KAVACH automatic train protection (ATP) system, which embeds ATS override capabilities, began rollout in 2023 on 1,548 route kilometers of South Central and North Central Railways, using radio-frequency identification (RFID) tags, telecom towers, and for real-time speed enforcement and collision avoidance. Following the June 2023 Balasore crash that killed over 280 people, expansions continued into 2025; as of October 2025, Kavach has been installed on approximately 1,465 route kilometers, with version 4.0 planned to cover 15,000 km of high-density routes, including Delhi-Mumbai and Delhi-Howrah corridors. South Korea's Korea Radio-based Train Control System (KRTCS-2), a wireless evolution of earlier KTCS frameworks dating to the late modernization efforts, employs LTE-R communication for continuous train supervision and automatic stops on conventional and high-speed lines, with prototypes tested at 350 km/h on the route since the 2010s. In Taiwan, the (TRA) adopted Ericsson's JZG 700 ATS system in the late 1970s, operational by 1979 on main lines, featuring inductive beacons for speed checks and automatic braking to handle dense urban traffic similar to Japan's ATS-SN. Across , ATS coverage is near-universal on urban metros and high-speed networks, with 2024 initiatives in and ongoing upgrades in and prioritizing dense corridors for enhanced reliability.

Europe

In , automatic train stop systems have evolved within a patchwork of national legacies, increasingly unified under the (ETCS) framework to enhance interoperability across borders. The exemplifies early adoption of such technologies, with the Automatic Warning System (AWS) implemented on main lines starting in following the Harrow rail disaster, providing auditory and visual warnings to drivers approaching cautionary or danger signals, and enforcing a brake application if unacknowledged. Complementing AWS, the Train Protection and Warning System (TPWS) was trialed in 1996 and rolled out network-wide by 2003 as an overlay for automatic train protection, using trackside transmitters to trigger emergency braking for signals passed at danger or excessive speeds at permanent speed restrictions. On the London Underground, Communication-Based Train Control (CBTC) systems, such as Thales Seltrac on the since 2015, incorporate automatic train stop functionality through continuous radio communication for precise positioning and of movement authority limits. ETCS, a core component of the (ERTMS), standardizes automatic train protection across the continent, with Levels 1 and 2 enabling balise-based or radio-transmitted movement authorities that culminate in automatic stopping via the Driver Machine Interface (DMI) if speed or position thresholds are violated. By late 2024, ETCS was operational on approximately 15% of European infrastructure, with uneven progress on (TEN-T) corridors ranging from 6% to 22%, though deployment totals around 10,000-15,000 km including national extensions. In , migration from the legacy Transmission Voie-Machine (TVM) system on high-speed lines, such as the Paris-Lyon route upgraded in late 2024, integrates ETCS as a parallel overlay to maintain compatibility until at least 2030, prioritizing lines like for full transition. National systems persist alongside ETCS, including Germany's Punktförmige Zugbeeinflussung (PZB), an inductive intermittent cab signaling introduced in the 1930s as Indusi, which enforces speed checks and automatic braking at signals via track magnets. In Italy, the Blocco Automatico a Correnti Codificate (BACC) provides train protection on 3 kV DC electrified lines through coded track circuits for cab signaling and overspeed prevention, evolving toward balise integration in the Sistema Controllo Marcia Treno (SCMT). Recent developments underscore standardization push, with the 2024 TEN-T (EU 2024/1679) mandating ETCS on all new, upgraded, or renewed core network lines by 2030 to foster and phase out national silos, supported by accelerated funding under the Connecting Europe Facility. By 2025, ETCS covers over 70% of high-speed in leading nations like and , with legacy ATS systems gradually decommissioned on TEN-T routes to enable seamless cross-border operations.

Other regions

In , Automatic Train Stop (ATS) systems, often integrated as Automatic Train Protection (ATP), exhibit significant state-based variations, with ongoing trials and legacy implementations tailored to urban and regional needs. has advanced ETCS Level 2 trials since 2019 as part of the project, utilizing (CBTC) for full automation and ATP enforcement across 36 km of driverless operations. In , legacy ATP was installed on the Tilt Train fleet following the 2004 derailment, becoming operational by mid-2005 to enforce speed restrictions and prevent overspeeding on tilting services between and . Victoria employs the Train Protection and Warning System (TPWS) for regional and suburban lines, with retrofits commencing in 2004 on Regional Fast Rail corridors and expanding to Melbourne's metro network from 2010 to mitigate incidents. New Zealand's adoption of ATS remains limited, primarily confined to the Wellington commuter network operated by KiwiRail, where an upgraded signaling system incorporates automatic train protection as a hybrid mechanical-electronic overlay on existing interlockings to enhance safety on the electrified Hutt Valley and Kapiti lines. In Latin America, Argentina's Roca Line introduced an early variant of the French Crocodile train protection system in 1985 on its electrified branches from Buenos Aires to La Plata and Ezeiza, providing inductive loop-based overspeed and signal enforcement to support suburban commuter services. The Buenos Aires Subway (Subte) has progressively implemented ATP across its lines, with Line D completing a full signaling upgrade in early 2025 to replace legacy systems with modern ATP for automated braking and train separation, funded partly by international loans to achieve Grade of Automation 2 compatibility. In Brazil, CBTC systems serving as integrated ATP are deployed on major metros, such as São Paulo's Line 4, where Siemens' Trainguard MT enables moving-block operations and automatic protection since 2022, reducing headways to 75 seconds while preventing collisions on high-density urban routes. South Africa's Passenger Rail Agency of South Africa (PRASA) conducted ATP pilots in the as part of broader signaling modernization, testing integrated train protection on commuter lines in and to address collision risks amid aging infrastructure, though full rollout has been delayed by funding constraints. Developments in 2025 emphasize standardization, with Australia's National Rail Action Plan driving mandatory ETCS standards through the Rail Industry Safety and Standards Board (RISSB), including AS 7711 for signaling principles and AS 7666 for train protection control, aiming for nationwide ATP harmonization beyond urban areas where coverage remains sparse. In August 2025, Australian transport ministers agreed to adopt ETCS as the unified signaling standard for on key routes.

References

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