Positive train control

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

Overview

The main concept in PTC (as defined for North American Class I freight railroads) is that the train receives information about its location and where it is allowed to safely travel, also known as movement authorities. Equipment on board the train then enforces this, preventing unsafe movement. PTC systems may work in either dark territory or signaled territory and may use GPS navigation to track train movements. The Federal Railroad Administration has listed among its goals, "To deploy the Nationwide Differential Global Positioning System (NDGPS) as a nationwide, uniform, and continuous positioning system, suitable for train control."

The American Railway Engineering and Maintenance-of-Way Association (AREMA) describes Positive Train Control as having these primary characteristics:

• Train separation or collision avoidance
• Line speed enforcement
• Temporary speed restrictions
• Rail worker wayside safety.

Various other benefits are sometimes associated with PTC such as increased fuel efficiency or locomotive diagnostics, however these are benefits that can be achieved by having a wireless data system to transmit the information, whether it be for PTC or other applications.

In the 1990s, Union Pacific Railroad had a partnership project with General Electric to implement a similar system known as "Precision Train Control." This system would have involved moving block operation, which adjusts a "safe zone" around a train based on its speed and location. The similar abbreviations have sometimes caused confusion over the definition of the technology. GE later abandoned the Precision Train Control platform.

U.S. Rail Safety Improvement Act of 2008

Background

Starting in 1990 the National Transportation Safety Board (NTSB) counted PTC among its "Most Wanted List of Transportation Safety Improvements." At the time, the vast majority of rail lines relied on the human crew for complying with all safety rules, and a significant fraction of accidents were attributable to human error.^{[citation needed]}

In September 2008, 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 the legislative process 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 September 12, 2008 in California, 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 issued a statement in support of the bill. President George W. Bush signed the 315-page Rail Safety Improvement Act of 2008 into law on October 16, 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 Federal Railroad Administration (FRA) published final regulations for PTC systems on January 15, 2010.

In December 2010 the U.S. Government Accountability Office (GAO) reported that Amtrak and the major Class I railroads have taken steps to install PTC systems under the law, but the work may not be complete by the 2015 deadline. The railroads and their suppliers are continuing to develop software to test various system components, which could delay equipment installation. GAO also suggests that publicly-funded commuter railroads will have difficulty in obtaining funds to pay for their system components.

As of January 2012, the U.S. Congress is considering bills that would extend the 2015 deadline of the Rail Safety Improvements Act, possibly granted the railroads an extension of several years. The AAR has indicated its support of the extension; at least one commuter rail operation, the SCCRA's Metrolink, has indicated opposition to any extension.

Controversy

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 US$10 billion, there are questions to the reliability and maturity of the technology for all forms of mainline freight trains and high density environments. 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 U.S. railroads over a 12-year period, 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 Class I railroads. Therefore, PTC was not economically justified at that time. The FRA concurred with this cost assessment in its 2009 PTC rulemaking document.

The reason behind the lack of economic justification is that the majority of accidents are minor and FRA crash worthiness standards help mitigate the potential loss of life or release of hazardous chemicals. For example in the 20 years between 1987 and 2007 there were only two PTC preventable accidents with major loss of life (16 deaths in the Chase, Maryland wreck (1987) and 11 in the Silver Spring, Maryland wreck (1996)) and in each case the causes of the accidents were addressed through changes to operating rules.

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.

Optionally, three additional components may exist:

• An on board navigation system and track profile database to enforce fixed speed limits
• 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 on board 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 in 2007 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. 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 trains 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.

Most current PTC implementations use the speed control unit to also store a database of track profiles attached to some sort of navigation system. The unit keeps track of the train's position along the rail line and automatically enforces any speed restrictions as well as the maximum authorized speed. Temporary speed restrictions can be updated before the train departs its terminal or via wireless data links. The track data can also be used to calculate braking curves based on the grade profile. The navigation system can use fixed track beacons or differential GPS stations combined with wheel rotation to accurately determine the train's location on the line accurately within a few feet.

Centralized control

While some PTC systems interface directly with the existing signal system, others may maintain a set of vital computer systems at a central location that can keep track of trains and issue movement authorities to them directly via a wireless data network. This is often considered to be a form of Communications Based Train Control and is not a necessary part of PTC.

Trackside device interface

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. Another capability would be to allow maintenance foremen the ability to automatically give trains permission through their work zones via a wireless device instead of verbal communications.

Technical limitations

Even where safety systems such as cab signaling have been present for many decades, the freight railroad industry has been reluctant to fit speed control devices due to the often heavy-handed nature of such devices having an adverse effect on otherwise safe train operation. The advanced processor-based speed control algorithms found in PTC systems claim to be able to properly regulate the speed of freight trains over 5,000 feet (1,500 m) in length and weighing over 10,000 short tons (9,100 t), but concerns remain about taking the final decision out of the hands of skilled locomotive engineers. Improper use of the air brake can lead to a train running away, derailment, or unexpected separation.^{[citation needed]}

Furthermore, an overly conservative PTC system runs the risk of slowing trains below the level at which they had previously been safely operated by human engineers. Railway speeds are calculated with a safety factor such that slight excesses in speed will not result in an accident. If a PTC system applies its own safety margin then the end result will be an inefficient double safety factor. Moreover a PTC system might be unable to account for variations in weather conditions or train handling and might have to assume a worst case scenario, further decreasing performance. In its 2009 regulatory filing, the FRA stated that PTC was in fact likely to decrease the capacity of freight railroads on many main lines. The European LOCOPROL/LOCOLOC project had shown that EGNOS-enhanced satellite navigation alone was unable to meet the SIL4 safety integrity required for train signaling.

From a purely technical standpoint, PTC will not prevent certain low speed collisions caused by permissive block operation, accidents caused by trains "shoving" in reverse, derailments caused by track or train defect, grade crossing collisions, or collisions with previously derailed trains. Where PTC is installed in absence of track circuit blocks it will not detect broken rails, flooded tracks, or cars that have been left or rolled onto the line.^{[citation needed]}

Wireless Issues

The wireless infrastructure planned for use by most North American freights and commuter railroads is based on a single frequency-band approach using 220 MHz spectrum. There are significant risks with this approach. First, the 220 MHz spectrum needed by the railroads is not currently available in sufficient quantity, especially in urban areas. There is also concern from several stakeholders in both the broadcast television industry and the Automated Maritime Telecommunications System (AMTS) industry regarding reallocating additional 220 MHz spectrum for the railroads. The Federal Communications Commission (FCC) has granted some waivers regarding previously-procured PTC 220 MHz licenses. However, so far the FCC has not ruled regarding reallocating the desired additional 220 MHz spectrum to the railroads. Recently, the FCC has started suggesting railroads focus on acquiring the required PTC spectrum on the secondary markets (leasing spectrum). This may be an indication that there is no near-term plan by the FCC to reallocate 220 MHz spectrum to the railroads. Unfortunately, it is likely that in some congested markets, the necessary 220 MHz spectrum is not available for leasing. This will likely lead some railroads to reevaluate their commitment to using only 220 MHz for PTC. There are several LMR bands that may individually, or in combination, provide enough spectrum through sale or leasing to support PTC in crowded urban areas. Implementing PTC at VHF (~160 MHz), UHF (~450MHz) VHF low band (~45MHz) or UHF (~900 MHz) are likely alternatives.

A second risk with the current wireless plan for North American PTC is that the single frequency-band approach to supporting real-time train control has a history of being difficult to use for such applications. This difficulty is not unique to train control. Interference, both man-made and natural, can at times affect the operation of any wireless system that relies on one frequency band. When such wireless systems are employed for real-time control networks it is very difficult to ensure that network performance will not sometimes be impacted. CSX encountered this problem when it experienced propagation ducting problems in its 900 MHz Advanced Train Control System (ATCS) network in the 1990s. The ATCS protocol, which the Association of American Railroads (AAR) had recommended the FCC consider as PTC in 2000 (when AAR sought a nationwide 900 MHz "ribbon" license), can support train control operation at both 900 MHz and 160 MHz. However, to date the latter frequency band is only used for ATCS on a few subdivisions and shortlines. More recently, the industry had been moving toward a more robust multi-band radio solution for data applications such as PTC. In 2007, BNSF first won FRA approval for their original ETMS PTC system using a multi frequency-band radio. In addition, in mid-2008, an FRA sponsored effort by the AAR to develop a Higher Performance Data Radio (HPDR) for use at 160 MHz actually resulted in a contract being awarded to Meteorcomm for a 4-band radio to be used for voice and data. These more recent multi-band radio efforts were shelved in late 2008, after the Rail Safety Improvements Act became law, and the freights decided to pursue PTC using 220 MHz alone, in a single frequency-band configuration. Amtrak and most commuter operations quickly followed suit, selecting 220 MHz, in part because they believed it was the easiest way for their PTC solutions to be interoperable with the freights.

A third identified risk with the current wireless plan applies mostly to the North American commuter rail agencies and the PTC protocols they have decided to use with 220 MHz radios. Soon after the Rail Safety Act was passed, many commuter railroads chose not to develop their own PTC protocol and instead decided to save time and money by using a protocol developed for either freight or long haul passenger (Amtrak) operations. Deploying such a protocol for urban commuter operation, where it will be necessary to support numerous, small, fast-moving trains, will be a challenge. It remains to be seen whether the performance envelope of PTC protocols developed and optimized for less numerous, slower and/or larger trains can support a more complex operational scenario, such as that of a commuter rail operation, without impacting on-time performance.

Additional technical challenges will face the railroads as they attempt to procure enough 220 MHz radios to deploy PTC on 70,000 miles (110,000 km) of right-of-way and on all of the associated locomotives and passenger trainsets. There are only two modest sized radio manufacturers, Meteorcomm and GEMDS, who have been identified as suppliers of the required 220 MHz radios. Meeting the procurement needs of the rail industry in support of the federally mandated 2015 deployment deadline may be difficult. As the delay continues at the FCC on deciding whether to displace incumbent 220 MHz licensees, address interference concerns in the television industry, and then reallocate 220 MHz spectrum to PTC, many railroads (in particular commuters) are in a holding pattern of sorts. They are hesitant to procure spectrum on the secondary markets if there is a chance they can license it themselves. Unfortunately, the window of opportunity for the entire industry to successfully procure enough 220 MHz radios and deploy and test them before the deadline occurs may be closing fast.

A large group of industry experts from the federal government, manufacturers, railroads, and consultants are participating in a study group sponsored by the IEEE 802.15 working group, to look at using lessons learned in protocol development in the IEEE 802 suite to propose a comprehensive solution to the wireless component of PTC. The solution could possibly include the current 220 MHz development efforts of the railroads as components to a broader approach to PTC, thus ensuring continuity. The end result may provide a way forward for all of the railroads to eventually deploy a more robust, reliable, future-proof, and scalable solution for the wireless component of PTC.

Areas where in use

Various types of Collision Avoidance Systems have been implemented across the globe. Most if not all of these operate differently than PTC in North America, as described above.

This list is incomplete; you can help by expanding it.

KLUB-U

The Russian KLUB-U train control system is similar to Positive Train Control for its integration of GLONASS satellite-based train location, electronic track map distribution and digital radio (GSM-R or TETRA) usage for track-releases as well as remote initiation of train stops. GE Rail has cooperated with the Russian VNIIAS manufacturer on this system. The KLUB-U system is used widely in the Russian Federation including high-speed rail for the Sapsan.

ERTMS (Europe)

Some form of Automatic Train Protection (ATP) has been operational in Europe for over one hundred years like the Automatic Train Control (ATC) system. In 1956 Automatic Warning System (AWS) was introduced in the United Kingdom whilst today the rail network is fitted with Train Protection & Warning System (TPWS). Some of the first systems implementing full ATP functionality were designed for the dedicated high speed rail lines such as the French TVM and German LZB. Continuing with the success of ATP systems, Europe is today transitioning to one ATP standard, the European Rail Traffic Management System (ERTMS), which is well evolved as a result of many years of European ATP experience and development. Although a major driver for the implementation of ERTMS is European interoperability, many non-European countries such as Australia, China, India, Saudi Arabia, South Korea and Libya are introducing ERTMS as the ATP system of choice.

The two main components of ERTMS are the European Train Control System (ETCS), a standard for in-cab train control, and GSM-R, the GSM mobile communications standard for railway operations. The equipment can further be divided between on-board and infrastructure equipment. There is also a low-cost variant ERTMS Regional developed by Banverket and the IUC. The ITARUS-ATC is a hybrid of the Russian KLUB-U in-cab signaling and the Itialian ERTMS Level 2 GSM-R block control.

The system authority for ERTMS is the European Railway Agency.

Alaska Railroad (ARRC)

Ansaldo STS USA Inc is working with the ARRC to develop a collision-avoidance, Vital PTC system, for use on their locomotives. The system is designed to prevent train-to-train collisions, enforce speed limits, and protect roadway workers and equipment. The microprocessor-based onboard control system is also designed to work with the Ansaldo STS USA Inc 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. An onboard computer alerts workers to approaching restrictions and to stop the train if needed.

Amtrak

Alstom's and PHW's Advanced Civil Speed Enforcement System (ACSES) system is installed on Amtrak’s Northeast Corridor between Washington and Boston. ACSES enhances the cab signaling systems provided by PHW Inc. 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.

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 (153 km/h), and eventually to 110 mph (180 km/h).

BNSF

Wabtec's Electronic Train Management System, (ETMS) is installed on a segment of the BNSF Railway. 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.

CSX

CSX Transportation is developing a Communications-Based Train Management (CBTM) system to improve the safety of its rail operations. CBTM is the predecessor to ETMS.

New Jersey Transit

Ansaldo STS USA Inc'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.

Union Pacific (UP)

A team of Lockheed Martin, Wabtec, and Ansaldo STS USA Inc installed a PTC system on a 120-mile segment of UP track between Chicago and St. Louis. An Indian IT Major software company Mahindra Satyam is also one of the strategic IT partners in development of PTC systems.

Manufacturers

This list is incomplete; you can help by expanding it.

Several companies make equipment for PTC systems, including:

• Alstom
• Ansaldo STS
• Argenia Railway Technologies Inc
• ARINC
• Bombardier Transportation
• Capital Tower & Communications
• Convergent Communications Inc
• Enterprise Integration
• Dixie Precast
• GE Transportation
• IBM
• Invensys
• Larsen Antennas
• Lilee Systems
• Lockheed Martin
• PHW Inc
• Quantum Engineering (now part of Invensys)
• Siemens
• Thales Group
• RF Innovations Pty Ltd
• Safetran
• TPSC Transportation Products
• Tunnel Radio of America
• Wabtec
• Western Towers
• Westinghouse Air Brake Company

See also

• Train protection system

References

• NTSB Symposium on Positive Train Control Systems (2005). Agenda and Presentations.
• Vantuono, William (March 2004). "BNSF starts positive train control trial - North American Viewpoint". International Railway Journal (Simmons-Boardman). ISSN 0744-5326. http://findarticles.com/p/articles/mi_m0BQQ/is_3_44/ai_114629906/. 

External links

• NTSB Safety Recommendation regarding 1996 Silver Spring accident (August 28, 1997)
• BNSF promotional video on ETMS
• "Communications-Based Signaling (CBS) – Vital PTC", Paper presented at AREMA C&S Technical Conference May 22, 2007