Positive train control

Positive train control

Positive train control (PTC) is a system of monitoring and controlling train movements to provide increased safety.


The main concept in PTC is that the train receives information about its location and where it is allowed to safely travel. Equipment on board the train then enforces this, preventing unsafe movement. Contrast this with conventional railway signaling in which equipment located along the track provides the information, and the engineer (driver) supplies the enforcement.

The basic functions of a PTC system are [ [http://transportation.northwestern.edu/programs/sandhouse/sources/presentations/resor_PTC_041304.pdf/ The Business Benefits of PTC] ] :
*manage track occupancies through centralized route and interlocking logic
*issue movement authorities via wireless data links to trains and work vehicles
*determine the position of trains
*enforce permanent and temporary speed limits
*enforce limits of movement authority (LoMA) for trains

Optionally, a PTC system can also include:
*pacing to optimize fuel economy
*monitor and control wayside systems
*report train diagnostics, alarms and operating parameters
*exchange instructions and messages between dispatcher and train


The NTSB has PTC on its Most Wanted List of Transportation Safety Improvements. [ [http://www.ntsb.gov/Recs/mostwanted/index.htm NTSB Most Wanted List of Transportation Safety Improvements - Implement Positive Train Control Systems] ]

The Rail Safety Advisory Committee (RSAC) identified nearly a thousand “PPAs” (PTC preventable accidents) on U.S. railroads over a 12-year period. Cost analysis determined the savings to be realized from each avoided accident, with the conclusion that PTC was economically justified. [http://transportation.northwestern.edu/docs/2004/2004.04.13.Resor.Presentation.pdf]

In Sept 2008, the US Congress considered a new rail safety law that sets a deadline of 2015 for implementation of positive train control (PTC) technology across most of the U.S. rail network. The bill, ushered through Congress by the Senate Commerce Committee and the House Transportation and Infrastructure Committee, was developed in response to the collision of a Metrolink passenger train and a Union Pacific freight train Sept. 12 in California, which resulted in the deaths of 25 and injuries to more than 135 Metrolink passengers.

Among its provisions, the law would provide funding to help pay for the development of PTC technology, limits the number of hours freight rail crews can work each month, and requires the Department of Transportation to determine work hour limits for passenger train crews.

The Association of American Railroads (AAR) has posted a rail industry response on its web site. A letter from AAR President and CEO Edward Hamburger states, in part,

"The legislation sets an aggressive deadline of 2015 for implementation of positive train control (PTC) across most of the rail network. The scope of the work remaining to be accomplished presents a challenge to both the supply industry and the railroads.

"Nonetheless, the freight railroad industry is committed to doing everything it can to ensure that PTC is implemented effectively and safely. We will work with the Federal Railroad Administration and our partners in the transit community, at Amtrak, our suppliers and our customers to implement the mandate."

For more information, view the AAR site and its special information section PTC - Get All The Facts at www.aar.org.

Basic operation

A typical PTC system involves three basic components:
*Equipment on the locomotive
*Equipment at the control center
*Bi-directional wireless data link between the train and the control centerOptionally, two additional components may exist:
*Wayside equipment
*Unidirectional data link between wayside equipment and train

Equipment on the locomotive

A GPS receiver on the locomotive receives position information. Alternatively, a transceiver is used to read transponders located on the track to locate the train's position. A data radio provides communications between the train and the control center and, optionally, with wayside devices. An onboard computer and display device displays information to the locomotive engineer (driver).

Equipment at the control center

A data radio provides communications between the control center and the train. Microprocessor-based central interlocking equipment performs safety logic.

Bi-directional wireless link

A wireless communications link allows required data to be passed between the control center and train.

How it works - the basics

The train reports its position to the control center via the wireless data link. The control center's safety interlocking logic uses the data from all trains to issue limits of movement authority (LoMA) and speed limits to each train, being careful to keep safe separation between trains. The train's onboard computer monitors the LoMA and speed limit data against actual train location and speed to determine potential and actual unsafe conditions. If the train is approaching the end of its LoMA or it is nearing its speed limit, the onboard computer warns the engineer, who is expected to take appropriate action. If the train passes the end of its LoMA, the onboard computer automatically signals for a safety brake application to bring the train to a stop. Similarly, if the train exceeds its allowed speed limit, the brakes are applied to stop the train. The onboard computer also monitors various locomotive systems such as power and brakes, and automatically sends diagnostic and alarm data to the control center when appropriate.

How it works - options

The train may be able to detect the status of (and sometimes control) wayside devices, for example switch positions. This information is sent to the control center to further define the train's safe movements. Text messages and alarm conditions may also be automatically and manually exchanged between the train and the control center.

PTC patent

A US patent has been granted for a distributed positive train control system to the Westinghouse Air Brake Company (WABCO). [ [http://www.freepatentsonline.com/5950966.html US Patent 5950966] ]

Where PTC is used

Various PTC systems have been implemented in a number of locations.


PTC-like systems are the rule on most European railroads, e.g. the Automatic Warning System in Great Britain, Punktförmige Zugbeeinflussung and Linienzugbeeinflussung systems in Germany, and Le Crocodile in France.

Alaska Railroad (ARRC)

Quantum Engineering Inc. installed its Train Sentinel system, a collision-avoidance, PTC system, on ARRC locomotives. The system is designed to prevent train-to-train collisions, enforce speed limits, and protect roadway workers and equipment. The microprocessor-based train-control system couples with Engesis' dispatching system to provide train control and dispatching operations from Anchorage.

Data between locomotive and dispatcher is transmitted over a digital radio system provided by Meteor Communications Corp. The train crew is able to see moving maps, grade, curvature, wayside device location and braking distance. GPS is used for positioning, and an onboard computer alerts workers to approaching restrictions and to stop the train if needed. [cite news |title=Alaska Railroad to install positive train-control system |url=http://www.progressiverailroading.com/freightnews/article.asp?id=3021 |publisher=Progressive Railroading |date=2003-08-27 |accessdate=2007-06-19 ]


ALSTOM's Advanced Civil Speed Enforcement System (ACSES) system is installed on AMTRAK’s Northeast Corridor between Washington and Boston. ACSES enhances the cab signaling system. It uses passive transponders to enforce permanent civil speed restrictions. The system is designed to prevent train-to-train collisions (PTS), protection against overspeed and protect work crews with temporary speed restrictions. [cite news |title=Advanced Civil Speed Enforcement System (ACSES) |url=http://www.alstomsignalingsolutions.com/OurProducts/PositiveTrainControl/ACSES/ |publisher=ALSTOM Signaling |date=2003 |accessdate=2007-11-17 ]

GE Transportation Systems' Incremental Train Control System (ITCS) is installed on Amtrak's Michigan line, allowing trains to travel at speeds up to 95 mph, and eventually to 120 mph. [cite news |title=AGE’s Positive Train Control Technology is Full Speed Ahead on Amtrak’s Michigan Line |url=http://www.getransportation.com/na/en/docs/919677_2005_10_ITCS.pdf |publisher=General Electric press release |date=2005-10-11 |accessdate=2007-09-21 ]

Burlington Northern Santa Fe (BNSF)

Wabtec's Electronic Train Management System, (ETMS) is installed on a segment of the BNSF. It is an overlay technology that augments existing train control methods. ETMS uses GPS for positioning and a digital radio system to monitor train location and speed. It is designed to prevent certain types of accidents, including train collisions. The system includes an in-cab display screen that warns of a problem and then automatically stops the train if appropriate action is not taken. [cite news |title=FRA Approves Positive Train Control System at BNSF |url=http://www.apta.com/passenger_transport/thisweek/070122_4.cfm |publisher=American Public Transportation Association |date=2007-01-22 |accessdate=2007-06-19 ]


CSX Transportation is developing a Communications-Based Train Management (CBTM) system to improve the safety of its rail operations. [cite news |title=Advances At CSX Intermodal
url=http://www.forbes.com/2006/07/13/csx-train-truck-intermodal-cx_rm_0713csx.html |publisher=Forbes |date=2006-07-13 |accessdate=2008-07-28

New Jersey Transit

US&S's Advanced Speed Enforcement System (ASES) is being installed on New Jersey Transit commuter lines. It is coordinated with ALSTOM's ACSES so that trains can operate on the Northeast Corridor. [cite news |title=ASES ProjectUpdate-March 2005 |http://www.ntsb.gov/Events/symp_ptc/presentations/05_Vogler.pdf |publisher=New Jersey Transit |date=2005-03-15 |accessdate=2007-09-21 ]

Union Pacific (UP)

A team of Lockheed Martin, Wabtec, and Union Switch & Signal installed a PTC system on a 120-mile segment of UP track between Chicago and St. Louis. [cite news |title=Lockheed Martin team wins PTC contract - positive train control system, Union Pacific |url=http://findarticles.com/p/articles/mi_m1215/is_7_201/ai_64337944 |publisher=Railway Age |date=2000-07 |accessdate=2007-06-19 ]

Companies with PTC systems

* [http://www.alstomsignalingsolutions.com/OurProducts/PositiveTrainControl/ ALSTOM]
* [http://www.arinc.com/products/intel_trans_sys/positive_train_ctrl.html/ ARINC]
* [http://www.getransportation.com/na/en/itcs.html GE Transportation Systems]
* [http://www.lockheedmartin.com/wms/findPage.do?prfr=false&dsp=fec&ci=11418&sc=400/ Lockheed Martin]
* [http://www.phwinc.com/ PHW Inc.]
* [http://www.qei.biz/PDF%20files/AKRR%20press%20rel.pdf/ Quantum Engineering]
* [http://grouper.ieee.org/groups/railtransit/wg2/Archive%20Other/2007%20AREMA%20CBS%20paper%20Vital%20PTC%20V2.pdf Safetran]
* [http://www.switch.com/carborne/digitrac.html/ Union Switch & Signal]
* [http://www.apta.com/passenger_transport/thisweek/070122_4.cfm/ Wabtec]
* [http://danger-ahead.railfan.net/reports/rep99/wesths_pos_train_control.html Westinghouse Air Brake]

ee also

*Cab signaling
*Railway signaling


External links

* [http://www.ntsb.gov/Recs/letters/1997/R97_39_42.pdf NTSB Safety Recommendation (August 28, 1997)]
* [http://www.ntsb.gov/TC/archive/RPH701_200503_Archive.htm NTSB Symposium: Positive Train Control Systems (March 2–3, 2005)]
* [http://findarticles.com/p/articles/mi_m0BQQ/is_3_44/ai_114629906/ BNSF starts positive train control trial - North American Viewpoint]
* [http://s3.amazonaws.com/trainmedia/video/etms.mpg BNSF promotional video on ETMS]

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