Cab signalling
In North America, the coded track circuit system developed by the Pennsylvania Railroad (PRR) and Union Switch & Signal (US&S) became the de facto national standard.
The train-control component of ERTMS, termed European Train Control System (ETCS), is a functional specification that incorporates some of the former national standards and allows them to be fully interoperable with a few modifications.
All cab signalling systems must have a continuous in-cab indication to inform the driver of track condition ahead; however, these fall into two main categories.
These and other such systems provide constant reminders to drivers of track conditions ahead, but are only updated at discrete points.
This is popular for early intermittent systems that used the presence of a magnetic field or electric current to designate a hazardous condition.
Continuous inductive systems include the two-aspect General Railway Signal Company "Automatic Train Control" installed on the Chicago and North Western Railroad among others.
Some of the first users of AF cab signal systems include the Washington Metro and Bay Area Rapid Transit.
Transponder based systems make use of fixed antenna loops or beacons (called balises) that transmit datagrams or other information to a train as it passes overhead.
Later, many railways and rapid transit systems would dispense with miniature in-cab signals in favour of an indication of what speed the operator was permitted to travel at.
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.
The Chicago, Milwaukee, St. Paul and Pacific Railroad had a 3-aspect system operating by 1935 between Portage, Wisconsin and Minneapolis, Minnesota.
[7] 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.
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.
Amtrak uses the Advanced Civil Speed Enforcement System (ACSES) for its Acela Express high-speed rail service on the NEC.
[8] 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.
