Cab Signalling - Cab Signalling Systems in The US

Cab Signalling Systems in The US

Cab signalling in the United States was driven by a 1922 ruling by the Interstate Commerce Commission (ICC) that required 49 railroads to install some form of automatic train control in one full passenger division by 1925. While several large railroads, including the 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 signalling technology supplied by Union Switch and Signal.

In response to the PRR lead, the ICC mandated that some of the nation's other large railroads 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.

Several railroads chose the inductive loop system rejected by the PRR. These included the Central Railroad of New Jersey (installed on its Southern Division), the Reading Railroad (installed on its Atlantic City Railroad main line) and the New York Central. Both the Chicago Northwestern 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.

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, absolute stops and 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. 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.