Intermittent inductive automatic train stop: Difference between revisions

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{{Short description|Rail signaling equipment}}

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{{More footnotes|date=September 2014}}

{{One source|date=May 2024}}

{{Original research|date=May 2024}}

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{{Other uses|Automatic Train Stop}}

The '''intermittent inductive automatic train stop''' (also referred to as '''IIATS''' or just '''automatic train stop''' or '''ATS''') is a [[train protection system]] used in North American mainline railroad and rapid transit systems. It makes use of [[magnetic reluctance]] to trigger a passing train to take some sort of action. The system was developed in the 1920s by the [[General Railway Signal]] Company as an improvement on existing mechanical [[train stop]] systems and saw limited adoption before being overtaken by more advanced [[cab signaling]] and [[automatic train control]] systems. The system remains in use after having been introduced in the 1920s.

== Overview ==

[[Image:Coaster 2103-ATS-inductor.jpg|thumb|IIATS pickup on the leading truck of a [[Coaster (Sanrail Diegoservice)|San Diego Coaster]] [[F40PH]]]]

The technology works by having the state of a track mounted "''shoe"'' read by a receiver mounted to a [[bogie|truck]] on the leading locomotive or car. In the standard implementation the shoe is mounted to the [[railroad ties|ties]] a few inches outside the right hand running rail, although in theory the shoe could be mounted anywhere on the ties.<ref name="look at" /> The system is binary with the shoe presenting either an "''on"'' or "''off"'' state to the receiver. In order to be [[failsafe]] when the shoe is energized it presents an "''off"'' state to the receiver, while the non-energized state presents an "''on"'' state which triggers an action. This allows things like permanent speed restrictions or other hazards to be protected by non-active devices.

The receiver consists of a two coil electromagnet carefully aligned to pass about 1.5 inches above the surface of the inductor shoe. The inductor shoe consists of two metal plates set into a streamlined housing designed to deflect impacts of debris or misaligned receivers. The metal plates are connected through a [[Choke (electronics)|choke circuit]] in the body of the shoe. When the choke circuit is open magnetic flux in the receiver's primary coil is able to induce a voltage in the receiver's secondary coil which in turn triggers an action in the locomotive. When the circuit is closed the choke eliminates the magnetic field and the voltage induced by it allowing the locomotive to pass without activation. Where unconditional activation was desired specially shaped metal plates could be used in place of a fully functional shoe, however the design of the system can result in [[false positive|accidental activations]] when the train passes over switches or other metal objects in the track area.

The most common use case for the ATS system was to alert the [[railroad engineer]] of an impending hazard and if the alert was not acknowledged, stop the train by means of a full service application of the [[Railway brake|brakes]]. When attached to signals the shoe would be energized when the signal was displaying a "Clear"''clear'' indication. Any other signal indication would de-energize the shoe and trigger an alarm in the cab. If the engineer did not cancel the alarm within 5–8 seconds a penalty brake application would be initiated and could not be reset until the train came to a complete stop.<ref name="look at">{{Cite web|url=httphttps://www.railpac.org/2008/10/02/a-look-at-automatic-train-stop-ats/|title=A look at Automatic Train Stop (ATS) – RailPAC|date=2 October 2008 }}</ref> Unlike mechanical train stops or other train stop systems, IIATS was not generally used to automatically stop a train if it [[Signal passed at danger|passed a stop signal]] and in practice could not be used for this purpose as the shoes were placed only a few feet from the signal they protected and would not present sufficient [[braking distance]] for the train to stop.

On bi-directionally signaled lines two "''shoes"'' would be needed, one for each direction of travel as locomotives would only have a sensor to detect the shoes on one side of the train. The receivers can also be designed for easy removal to prevent damage when operating in non-equipped territory or to cut costs when only a small portion of the railroad requires ATS equipped locomotives. "''Inert"'' inductors are sometimes placed in advance of certain speed restrictions as an alert or at engine terminals to test the functionality of the ATS system.

On a few [[light rail]] lines IIATS has been employed in a manner similar to mechanical train stops, stopping the train if it passes an absolute stop signal. It is useful where light rail shares tracks with mainline railroad trains as mechanical trips may be damaged by or interfere with freight operations and because [[light rail vehicle]]s can be brought to a stop much more quickly than a mainline railroad train without requiring complex [[Overlap (railway signalling)|signal overlaps]]

== Use ==

[[Image:SJLR Induction-Stop.jpg|200px|right|thumb|IIATS shoe in service on the NJT [[RiverLINE]] to enforce absolute stops at [[interlocking]]s.]]

Starting in the 1930s the US [[Interstate Commerce Commission]], in its role as a federal railroad regulator, encouraged railroads to adopt new safety technologies to decrease the rate of railroad accidents. IIATS was offered by the General Railway Signal Company of [[Rochester, NY]] as one such technology and it was adopted by the [[New York Central]] railroad for use on its high speed [[Water Level Route]] between New York and Chicago and on a number of other lines. The [[Southern Railway (U.S.)|Southern Railway]] also chose to adopt ATS on most of its main lines eventually covering 2700 route miles. In addition the [[Chicago and North Western Railway]] installed the system on some of its Chicago area commuter lines.

After the [[Naperville train disaster]] caused by a missed signal, the ICC required additional technical safety systems for any train traveling at or above 80&nbsp;mph with the rule taking effect in 1951. Those railroads still interested in high speed operations IIATS met the minimum ICC requirements with a lower cost compared to [[Pulse code cab signaling|other cab signaling]] or automatic train control systems, however with rail travel facing increased competition from cars and airplanes most railroads simply choose to accept the new speed limit. Only the [[Atchison, Topeka and Santa Fe]] choose to fully equip its Chicago to Los Angeles and Los Angeles to San Diego main lines in support of the [[Super Chief]] and other premier high speed trains.

IIATS installations reached their peak in 1954 with a total of 8650 road miles, 14400 track miles, and 3850 locomotives equipped with the system. However, with the collapse of long distance passenger rail travel and the general North American railroad industry malaise in 1971, the bankrupt [[Penn Central]] was permitted to remove IIATS from its Water Level Route along with the Southern and other railroads with test or pilot IIATS systems. Even the ATSF and successor [[BNSF]] were gradually allowed by regulators to remove IIATS from parts of previously equipped lines due to the reduced passenger traffic. At the dawn of the 21st century the only IIATS equipped lines were the [[Metrolink (Southern California)|MetroLink]] and [[Coaster (commuter rail service)|Coaster]] line between San Diego and Fullerton,<ref name="look at" /> parts of the former ATSF Super Chief route in California, Arizona, New Mexico, Colorado, Kansas and Missouri and the former [[Chicago and North Western Railway]] [[Union Pacific North Line|North Line]], [[Union Pacific Northwest Line|Northwest Line]] out of Chicago operated by [[Union Pacific]] on behalf of [[Metra]]

When the [[New JerseyNJ Transit]] [[RiverLINERiver Line (NJ Transit)|River Line]] opened in 2004 it featured a new IIATS system. This is a light rail systems running on shared track with main line freight traffic and IIATS is used to enforce a full stop at equipped signals instead of as a warning system.

== See also ==