Editing Cab signalling (section)

== Cab signalling systems in the United States ==
Cab signalling in the United States was driven by a 1922 ruling by the [[Interstate Commerce Commission]] (ICC) that required 49 railways to install some form of automatic train control in one full passenger division by 1925.<ref>
{{citation
  | title = Railroad Operational Safety, Status and Research Needs
  | edition= Transportation Research Circular E-C085
  | date = January 2006
  | publisher = Transportation Research Board of the National Academies (United States)
  | url = http://www.trb.org/publications/circulars/ec085.pdf
  | page = 27
  | access-date = 2008-04-13
 }}
</ref>  While several large railways, including the  [[Atchison Topeka & Santa Fe|Santa Fe]] and [[New York Central]], fulfilled the requirement by installing intermittent inductive train stop devices, the PRR saw an opportunity to improve operational efficiency and installed the first continuous cab signal systems, eventually settling on [[pulse code cab signaling]] technology supplied by [[Union Switch and Signal]].

In response to the PRR lead, the ICC mandated that some of the nation's other large railways must equip at least one division with continuous cab signal technology as a test to compare technologies and operating practices. The affected railroads were less than enthusiastic, and many chose to equip one of their more isolated or less trafficked routes to minimize the number of locomotives to be equipped with the apparatus.

[[File:Amt 9634-CDU-closeup.jpg|thumb|upright|[[Amtrak]] ACSES-capable cab signal display unit showing both a miniature signal and associated speed limit.]]

Several railways chose the inductive loop system rejected by the PRR. These railways included the [[Central Railroad of New Jersey]] (installed on its Southern Division), the [[Reading Railroad]] (installed on its [[Atlantic City Railroad]] main line), the New York Central, and the [[Florida East Coast Railway|Florida East Coast]].<ref>{{cite web |title=Florida East Coast Signal Aspects |url=https://www.railroadsignals.us/rulebooks/fec/index.htm |website=www.railroadsignals.us |access-date=4 June 2020 |language=en}}</ref> Both the Chicago and North Western and [[Illinois Central]] employed a two-aspect system on select suburban lines near Chicago. The cab signals would display "Clear" or "Restricting" aspects. The CNW went further and eliminated the wayside intermediate signals in the stretch of track between Elmhurst and West Chicago, requiring trains to proceed solely based on the 2-aspect cab signals. The [[Chicago, Milwaukee, St. Paul and Pacific Railroad]] had a 3-aspect system operating by 1935 between [[Portage, Wisconsin]] and [[Minneapolis, Minnesota]].<ref>{{cite journal|url=https://books.google.com/books?id=wN8DAAAAMBAJ&q=milwaukee+road+hiawatha&pg=PA512|title=Steam Still Rules the Rails|journal=Popular Mechanics|volume=64|number=4|date=October 1935|pages=512–513|access-date=2010-02-11}}</ref>

As the Pennsylvania Railroad system was the only one adopted on a large scale, it became a de facto national standard, and most installations of cab signals in the current era have been this type.  Recently, there have been several new types of cab signalling which use communications-based technology to reduce the cost of wayside equipment or supplement existing signal technologies to enforce speed restrictions and absolute stops and to respond to grade crossing malfunctions or incursions.

The first of these was the Speed Enforcement System (SES) employed by [[New Jersey Transit]] on their low-density [[Pascack Valley Line]] as a pilot program using a dedicated fleet of 13 [[GP40PH-2]] locomotives.  SES used a system of transponder beacons attached to wayside block signals to enforce signal speed.  SES was disliked by engine crews due to its habit of causing immediate penalty brake applications without first sounding an overspeed alarm and giving the engineer a chance to decelerate.  SES is in the process of being removed from this line, and is being replaced with CSS.

[[Amtrak]] uses the [[Advanced Civil Speed Enforcement System]] (ACSES) for its ''[[Acela Express]]'' high-speed rail service on the NEC.<ref name="FRA-PTC">{{cite web| url=http://www.fra.dot.gov/us/content/1265| title=Positive Train Control Overview| author=United States Federal Railroad Administration| date=2009-02-20| access-date=2010-10-05| archive-url=https://web.archive.org/web/20100219144321/http://www.fra.dot.gov/us/content/1265| archive-date=2010-02-19| url-status=dead}}</ref> ACSES was an overlay to the existing PRR-type CSS and uses the same SES transponder technology to enforce both permanent and temporary speed restrictions at curves and other geographic features.  The on-board cab signal unit processes both the pulse code "signal speed" and the ACSES "civil speed", then enforces the lower of the two.  ACSES also provides for a positive stop at absolute signals which could be released by a code provided by the dispatcher transmitted from the stopped locomotive via a data radio.  Later this was amended to a simpler "stop release" button on the cab signal display.