Positive train control (PTC) is a family of automatic train protection systems deployed in the United States. Most of the United States' national rail network mileage has a form of PTC. These systems are generally designed to check that trains are moving safely and to stop them when they are not.
Positive train control restricts the train movement to an explicit allowance; movement is halted upon invalidation. A train operating under PTC receives a movement authority containing information about its location and where it is allowed to safely travel. PTC was installed and operational on 100% of the statutory-required trackage by December 29, 2020.
Overview The American Railway Engineering and Maintenance-of-Way Association (AREMA) describes positive train control systems as having these primary functions: Train separation or collision avoidance Line speed enforcement Temporary speed restriction enforcement Rail worker wayside safety Blind spot monitoring
History Background In the late 1980s, interest in train protection solutions heightened after a period of stagnant investment and decline following World War II. Starting in 1990, the United States National Transportation Safety Board (NTSB) counted PTC (then known as positive train separation) among its "Most Wanted List of Transportation Safety Improvements."National Transportation Safety Board (NTSB), Washington, DC (2010). "Modifications to NTSB Most Wanted List; List of Transportation Safety Improvements after September 1990." NTSB (2010). "NTSB Most Wanted List of Transportation Safety Improvements – Implement Positive Train Control Systems." At the time, the vast majority of rail lines in US relied upon crew members to comply with all safety rules, and a significant fraction of accidents were attributable to human error, as evidenced in several years of official reports from the Federal Railroad Administration (FRA).
In September 2008, Congress considered a new law that set a deadline of December 15, 2015 for implementation of PTC technology across most of the US rail network. The bill, ushered through the legislative process by the Senate Commerce Committee and the House Transportation and Infrastructure Committee, was drafted in response to the collision of a Metrolink passenger train and a Union Pacific Railroad freight train at September 12, 2008, in Los Angeles, which resulted in the deaths of 25 and injuries to more than 135 passengers.
As the bill neared final passage by Congress, the Association of American Railroads (AAR) issued a statement in support of the bill.Association of American Railroads, Washington, DC (2008-09-24). "Statement by Edward R. Hamberger, President and CEO Association of American Railroads on Passage of the Comprehensive Rail Safety Bill." Press release. President George W. Bush signed the 315-page Rail Safety Improvement Act of 2008 into law on October 16, 2008.U.S. Rail Safety Improvement Act of 2008, , , . Approved 16 October 2008.
Provisions of the law Among its provisions, the law provides 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.
Implementation
To implement the law, the FRA published initial regulations for PTC systems on January 15, 2010.FRA (15 January 2010). "Positive Train Control Systems; Final rule." Federal Register. The agency published amended regulations on August 22, 2014.FRA (2014-08-22). "Positive Train Control Systems (RRR)."
In December 2010, the Government Accountability Office (GAO) reported that Amtrak and the major railroads had taken steps to install PTC systems under the law, but commuter rail operators were not on track for the 2015 deadline. , only seven commuter systems (29 percent of those represented by APTA) were expecting to make the deadline. Several factors have delayed implementation, including the need to obtain funding (which was not provided by Congress); the time it has taken to design, test, make interoperable, and manufacture the technology; and the need to obtain radio spectrum along the entire rail network, which involves FCC permission and in some cases negotiating with an existing owner for purchase or lease.
The Metrolink commuter rail system in Southern California is planning to be the first US passenger carrier to install the technology on its entire system. After some delays,Weikel, Dan (24 January 2014) "Metrolink to replace contractor to avoid train control project delays" Los Angeles Times demonstration PTC in revenue service began in February 2014; the system is expected to be completed in late summer 2015.
In the Chicago metropolitan area, the Metra system expected it will not be fully compliant with the PTC mandate until 2019.
In October 2015, Congress has passed a bill extending the compliance deadline by three years, to December 31, 2018. President Barack Obama signed the bill on October 29, 2015. Only four railroads met the December 2018 deadline; the other 37 got extensions to December 2020, which was allowed under the law for railroads that demonstrated implementation progress. On December 29, 2020, it was reported that the safeguards had been installed on all required railroads, two days ahead of the deadline.
Cost-benefit analysis
There is some controversy as to whether PTC makes sense in the form mandated by Congress. Not only is the cost of nationwide PTC installation expected to be as much as , most all of it borne by U.S. freight railroads, there are questions as to the reliability and maturity of the technology for all forms of mainline freight trains and high density environments.FRA (21 July 2009). "Positive Train Control Systems; Notice of proposed rulemaking." Federal Register. The PTC requirement could also impose startup barriers to new passenger rail or freight services that would trigger millions of dollars in additional PTC costs. The unfunded mandate also ties the hands of the FRA to adopt a more nuanced or flexible approach to the adoption of PTC technology where it makes the most sense or where it is technically most feasible.
While the FRA Rail Safety Advisory Committee identified several thousand "PPAs" (PTC preventable accidents) on US railroads over a 12-year period, a 2004 cost analysis determined that the accumulated savings to be realized from all of the accidents was not sufficient to cover the cost of PTC across the railroads at that time.Resor, Randolph R. (2004). "The Business Benefits of PTC." {doubtful} Northwestern University Transportation Center, Evanston, IL. The FRA concurred with this cost assessment in its 2009 PTC rulemaking document.
The cost of implementing PTC on up to 25 commuter rail services in the United States has been estimated at over $2 billion and because of these costs, several services are having to cancel or reduce repairs, capital improvements, and service. Other services simply do not have the funds available for PTC and have deferred action assuming some change from Congress. Railroads that operate lines equipped with cab signalling and existing Automatic Train Control systems have argued that their proven track record of safety, which goes back decades, is being discounted because ATC is not as aggressive as PTC in all cases.
PTC preventable crashes PTC could have prevented some crashes. In 2013, a Metro-North derailment in the Bronx killed four people and injured 61. This crash was caused by excess speed, something PTC is capable of guarding against. In 2015, an Amtrak derailment in Philadelphia killed eight and injured 185. In this incident, the train accelerated beyond safe speed due to actions of a distracted engineer of the Amtrak train. According to the NTSB, this crash could have been prevented by a PTC system that would have enforced the speed limit and prevented the overspeed and subsequent crash of the train. In 2017, another Amtrak derailment near DuPont, Washington, killed three and injured 62. The engineer mistook the train's location, and therefore was not following proper restrictions, failing to notice signage that indicated the speed restrictions in the area. The NTSB learned safety improvements had recently been made to the track, except for the PTC section of the improvements. It was ultimately concluded that the engineer's error in train location lead to the crash. Sound Transit, the owner of the section of railway where the accident occurred, was in the process of installing PTC, but it was not operational at the time of the accident. In 2018, another collision occurred when Amtrak train rammed a stationary freight train in Cayce, South Carolina, killed two crew members and injured 116 others. Chairman of the NTSB, Robert Sumwalt, stated that "an operational PTC is designed to prevent this type of incident."
Basic operation A typical PTC system involves two basic components: Speed display and control unit on the locomotive A method to dynamically inform the speed control unit of changing track or signal conditions.Olson, R.T., Jr. (2007). "Incremental Train Control System On Amtrak's Michigan Line." Presentation at AREMA Annual Conference, 9–12 September 2007, Chicago, IL. Optionally, three additional components may exist: An on-board navigation system and track profile database to enforce fixed speed limits A bi-directional data link to inform signaling equipment of the train's presence Centralized systems to directly issue movement authorities to trains
PTC infrastructure There are two main PTC implementation methods currently being developed. The first makes use of fixed signaling infrastructure such as coded track circuits and wireless transponders to communicate with the onboard speed control unit. The other makes use of wireless data radios spread out along the line to transmit the dynamic information. The wireless implementation also allows for the train to transmit its location to the signaling system which could enable the use of moving or "virtual" blocks. The wireless implementation is generally cheaper in terms of equipment costs, but is considered to be much less reliable than using "harder" communications channels. , for example, the wireless ITCS system on Amtrak's Michigan Line was still not functioning reliably after 13 years of development, while the fixed ACSES system has been in daily service on the Northeast Corridor since 2002 (see Amtrak, below).
The fixed infrastructure method is proving popular on high-density passenger lines where pulse code cab signaling has already been installed. In some cases, the lack of a reliance on wireless communications is being touted as a benefit.Vogler, John (2005). Symposium on Positive Train Control Systems The wireless method has proven most successful on low density, unsignaled dark territory normally controlled via track warrants, where speeds are already low and interruptions in the wireless connection to the train do not tend to compromise safety or train operations.
Some systems, like Amtrak's ACSES, operate with a hybrid technology that uses wireless links to update temporary speed restrictions or pass certain signals, with neither of these systems being critical for train operations.
Locomotive speed control unit The equipment on board the locomotive must continually calculate the train's current speed relative to a speed target some distance away governed by a braking curve. If the train risks not being able to slow to the speed target given the braking curve, the brakes are automatically applied and the train is immediately slowed. The speed targets are updated by information regarding fixed and dynamic speed limits determined by the track profile and signaling system.