Pulse Code Cab Signaling

Amtrak cab display

The Pulse Code Cab Signaling is a train control system widely used in the USA. The term means " pulse-code-modulated cab signaling ". In the basic version, like the Italian RS4 Codici , it transmits four driving terms. This "4-aspect-system" was introduced by the Pennsylvania Railroad in the 1920s .

history

In 1922 the Interstate Commerce Commission decided that trains without automatic train control may not travel more than 80 miles per hour ( mph ) in the future . The Pennsylvania Railroad railway company took this as an opportunity to introduce continuous cab signaling and commissioned the supplier Union Switch & Signal with the development.

By 1927 the tests had progressed so far that one could define an advertisement with four driving terms. Originally the train driver was supposed to acknowledge the change with restrictions (without the acknowledgment automatic braking would have occurred), but later a speed monitoring system for the vehicles was developed for passenger operation ("Clear" = unlimited, "Approach Medium" = approach with up to 45 mph, "Approach" = slow approach with up to 30 mph, "Restricting" = shunting operation with up to 20 mph).

Pennsylvania Railroad then installed systems on its routes from Pittsburgh to Philadelphia and New York to Washington. Subsequent companies took over this train control and the system quickly developed into the de facto standard in the USA, including the extended and compatible systems.

function

There is a 100 in the rail Hz signal fed in, the feed following a pulse code. A keying of 180 pulses per minute stands for "Clear" (distance free / unlimited), 120 pulses per minute correspond to "Approach Medium" (slow down), 75 pulses per minute are "Approach" (slow approach) and 0 (no pulse ) for "Restricting" (maneuvering on sight).

This rough classification was not sufficient for some applications, for example in the dense traffic cycle of urban rapid transit systems and when heavy trains approach the frequent curves on mountainous routes. Another pulse code with 270 pulses per minute was introduced and, in parallel, pulses were sent at a frequency of 250 Hz. This allows more finely graduated speed specifications to be defined. Train control in the north-east corridor has been based on the following allocation since the 1990s:

100 Hz code	250 Hz code	Cab Signal Aspect	Cab signal speed	Notes
180	180	Clear	150 mph	Legacy Units get Clear (125 mph)
180	---	Clear	125 mph	Original PRR system code
270	270	Clear	100 mph	Used for high density signaling.
270	---	Cab speed	60 mph	Used for high density signaling. Compatible with LIRR ASC system
120	120	Cab speed	80 mph	Used for most high speed turnouts. Legacy Units get Approach Medium.
120	---	Approach medium	45 mph	Original PRR system code
75	---	Approach	30th mph	Original PRR system code
0	---	Restricting	20th mph	Failsafe state. Original PRR system code

Note the backward compatibility with the 4-aspect system - only when using the 270 keying does an incompatibility arise, but this is only used in the area of ​​the New York Penn Station , and there is derived from the use of the Long Island Rail Road trains.

Extensions

The pulse code system has been given various extensions, both for the operation of light rail networks and for high-speed traffic. However, these extensions are incompatible with one another; they only have the lowest common denominator with the 4-aspect system.

As a result of the railway accident at Chase in 1987, the function of the driver's cab was supplemented by a speed monitoring system LSL ("locomotive speed limiter") - while the signals usually only generate a warning tone that has to be acknowledged, a braking curve at the LSL is monitored by computer (compare PZB Restrictive Mode ).

In 2008, the US Congress demanded that a uniform train control system Positive Train Control (PTC) be introduced by 2015 (Rail Safety Improvement Act, published on 16. October 2008). There were discussions afterwards, as the resolution is an "Unfunded Mandate" (i.e. it does not include financial support from the federal budget), but the Federal Railroad Administration approved on 12. January 2010 clearly emphasized the positive cost-benefit ratio and obliged the railway companies to implement it.

In a statement by the AAR ( Association of American Railroads ) reference is made in this regard to the existing ACSES ( Advanced Civil Speed ​​Enforcement System ), which was installed by Amtrak for high-speed traffic in the Northeast Corridor (tested 2000–2002 between New Haven and Boston, hereinafter to Washington extended). That system is based on Eurobalises , but it has to be differentiated from the European ERTMS , as the driving terms of Pulse Code Cab Signaling currently have priority and no GSM-R is used. For freight transport in particular, it is also under discussion to dispense with position reports from balises and to work with differential GPS . These elements are then combined in a new type of PTC system.

Individual evidence

1. ↑ ^{a b} Archived copy ( memento of the original from January 19, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
2. ↑ http://www.aar.org/NewsAndEvents/PressReleases/2008/09/092408_Statement_on_railsafety_bill.aspx  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.