Joe Drapa is Senior Engineer at Transportation Technology Center Inc, Bill Moore Ede is Scientist, and Alan Polivka is Assistant Vice-President, Communications & Train Control Technologies.
EFFORTS TO develop effective and affordable communications-based train control systems - known amongst North American freight railroads as Positive Train Control - have been in progress since the early 1980s. A major milestone was achieved in December 2006 when the Federal Railroad Administration authorised BNSF to install Wabtec's Electronic Train Management System on sections of its 54 700 km network. ETMS uses GPS to locate trains, and will be applied by BNSF in both signalled and non-signalled territory.
ETMS is a communication-based train control (CBTC) system that issues safety critical information such as movement authorities, speed restrictions and the position of points in digital form by radio to the locomotive cab where it is displayed to the driver. The onboard computer marries this up with the train's location, provided by the Global Positioning System (GPS), and will automatically initiate braking if the train crew fails to respond appropriately to warnings to reduce speed or stop.
BNSF plans further installation of the system this year. This follows successful testing beginning in October 2004 on BNSF's Beardstown subdivision in Illinois. In a statement issued on January 8 2007 Federal Railroad Administrator Joseph H Boardman described the approval as 'a major achievement that marks the beginning of a new era of rail safety'.
This observation may reflect the fact that historically automatic train control, automatic train stop or cab signalling have only been mandated by law on passenger lines where speeds exceed 127 km/h. BNSF's move to apply PTC widely, together with continuing interest from other operators, indicates acceptance that the costs and benefits are at last moving into balance.
PTC technology has gained significant momentum of late, with numerous implementations being developed throughout the United States. Widescale adoption has the potential to improve safety, lower operational costs, improve service, and increase network capacity.
Communication-Based Train Control
Fig 1 explains the architecture and operation of a stand-alone office-centric CBTC system. The dispatcher grants trains and work crews permission to occupy sections of track using computer programmes to generate movement authorities and speed restrictions, collectively known as 'mandatory directives'. FRA defines these as any written 'movement authority or speed restriction that affects a railroad operation'.
In an office-centric system with centralised traffic control, mandatory directives are sent digitally to the CBTC office server which checks them for conflicts. They are then transmitted through the communications network to operate points and signals. Authorities and temporary speed restrictions are likewise transmitted to train crews who can view them using onboard displays, which also show fixed information such as route profiles and permanent (civil engineering) speed restrictions.
Trains send back location reports, and the points and signals report their status through the communications network to the office server.
The CBTC office system knows the location of all trains on the network and monitors the health and status of points, signals, and other field equipment. It also knows each train's makeup, speed, and movement authorities. The onboard equipment, having first warned the crew, can take control to stop a train in cases where the train crew does not or may not be able to do so.
Positive Train Control
PTC systems are a form of CBTC. To satisfy the three basic safety features specified by FRA's Railroad Safety Advisory Committee's PTC Working Group a PTC system must:
- prevent train-to-train collisions (positive train separation)
- enforce speed restrictions, including civil engineering restrictions and temporary speed restrictions
- provide protection for workers and their equipment who are granted possession of track under specific authorities.
The four Class I railroads in the USA currently developing PTC systems are BNSF, CSX, Norfolk Southern, and Union Pacific. In addition, FRA is currently funding development of Amtrak's Incremental Train Control System.
FRA is also funding the North American Joint Positive Train Control project. Najptc has benefited several of the PTC projects through the re-use and enhancement of significant portions of its open, non-proprietary onboard hardware and software designs, algorithms, user-machine interfaces, and safety analyses.
Two decades of development
Following a landmark meeting organised by AAR and RAC in Toronto in June 1984 (RG 8.84 p577), today's CBTC systems got their start two decades ago with the Advanced Train Control System - an effort supported by a number of railroads in the United States and Canada - and Burlington Northern's Advanced Railroad Electronics System.
While significant technical progress was achieved in each case, wide-scale adoption did not occur because at the time an acceptable business case could not be made in terms of operational efficiency and/or improved safety.
Since then, the major railroads have continued their interest in the technology and its capabilities, which have the potential to improve safety, increase operational efficiency and allow for higher-speed passenger operations.
There are two general groups of authority-granting methods in use by North American railroads: forms-based and signal-based. The former can be Direct Traffic Control, Track Warrant Control or variants of either. Collectively, these are known as Manual Block Systems or MBS control. The dispatcher gives trains authority to occupy blocks of territory, which may be a section of track between two stations, for example.
The term 'forms-based' means that in MBS the dispatcher's movement authorities are typically conveyed by voice radio to train crew, who copy them on paper. The crew then repeats the instructions back to the dispatcher for verification. The movement authority is only valid when the dispatcher confirms the repeat.
Centralised Traffic Control is the main signal-based method of controlling trains. CTC is typically used on medium or high density lines where the increase in traffic capacity can justify the additional cost of lineside signalling and remotely-operated points.
Railroads can also have MBS overlaid on Automatic Block Signalling as an alternative to CTC. The signals are operated locally by track circuits and only indicate whether block sections ahead are occupied or not.
CBTC can be implemented in one of three ways:
- as an overlay to an existing control system
- integrated with an existing control system
- as a stand-alone system.
When CBTC is designed as an overlay to CTC (Fig 2) it can be thought of as a 'safety overlay'. The underlying CTC system performs the vital lineside logic, verifies the integrity of the route set by the dispatcher and conveys authority. As such, CBTC only enforces the authority limits and speed restrictions and can be designed in a non-vital manner.
When used as an overlay to MBS, CBTC provides a 'safety net'. For example, by keeping track of movement authorities granted by a dispatcher, CBTC can warn train crews approaching a work zone, and apply the brakes if the crew fails to slow down. Ultimately, the underlying control system provides the authority, but CBTC mitigates the risk when an unsafe situation has been detected.
Within an integrated CBTC system, both the underlying system and CBTC verify and convey authority - the challenge is to ensure that both systems convey the same authority simultaneously. With this setup, CBTC enforces authorities and speed restrictions and must be designed as a vital system.
An integrated CBTC system may be deployed on CTC territory within which not all locomotives are equipped for CBTC. In this case, CBTC, through the cab display, and CTC through lineside signals would both provide the authority to locomotives equipped with CBTC, whilst CTC through the lineside signals would do so for locomotives that are not.
As a stand-alone system, CBTC plays the sole role in verifying, conveying, and enforcing authority, with the system designed to be vital. In this configuration, all trains and work crews receive their authority from the CBTC system. Table I is a summary of the capabilities of each PTC system currently in development.
Common to all of the North American CBTC freight applications is the use of GPS for train location, avoiding the need for track transponders or balises. The GPS applications vary in location accuracy and the quality of dead reckoning where signals from satellites are absent.
Modelling has shown that CBTC requires radio links that support high data throughput. Because of this, FRA is funding development of a higher-performance data radio that will integrate voice and data communications. This would be deployed at base stations, on-board locomotives, at lineside devices, and within mobile communication units used by roadway workers.
Union Pacific adopts CBTC
UP's PTC system being developed by Wabtec is called Communications Based Train Control. This will be a vital, integrated system that enforces authority limits and speed restrictions, monitors point position, and offers additional features such as automatic horn activation at crossings. It is designed to be integrated with cab signalling.
CBTC interfaces with UP's CAD III next-generation Computer Aided Dispatching system. CAD III provides real-time planning of train movements and employs a network-wide movement planner using extended time horizons. It is also intended to provide CBTC with pacing cues to train crews for fuel economy, and to relieve congestion.
UP is also integrating New York Air Brake's Leader system with CBTC to provide onboard train handling support and energy management reporting. Leader's onboard display shows the train driver actual in-train forces, track topology and train trajectory. In a proactive assist mode, it can recommend throttle and brake settings to the driver that will minimise fuel costs and reduce in-train forces. These features are expected to improve service reliability and reduce annual fuel consumption by 6% to 8%.
UP will test CBTC on MBS territory within its Spokane Subdivision, which operates under TWC, and on the South Morrill Subdivision, which has CTC. Both tests are scheduled to begin in August and will continue for two or three years. UP expects to apply to FRA in early 2009 for system-wide approval.
CSX trials CBTM
CSX's PTC system, also being developed by Wabtec, is known as Communications Based Train Management. CBTM is a safety overlay that can enforce authority limits and speed restrictions and monitor point position.
CBTM interfaces with CSX's Next Generation Dispatch technology. which provides CBTM with movement authorities, temporary speed restrictions, and conditional stop or work zone messages.
Fig 3 shows the driver's CBTM display. At this time, the display provides visual warning and braking messages to the crew but no authority information. These messages appear when a train approaches a point at which a speed restriction is in place, for example. The CBTM display also provides prompts, including an audio alert, to which the crew must respond in order to avoid enforced intervention.
In the event of enforcement, the train crew can use the onboard display to review movement authorities and train messages held by CBTM. The CBTM display can also show speed and tractive effort should the train driver's main display fail.
CSX field-tested CBTM from April 2000 to March 2004 on its Spartanburg Subdivision, which is under DTC control. This pilot programme identified reliability, affordability, and functionality issues that have since been addressed.
Currently, two enhancements are being made to CBTM. The first is a migration to a common software platform, which will provide graphical information to the crew through the onboard display. This platform was derived from the NAJPTC onboard platform and is the same as that being used by CBTC and ETMS. The second enhancement is to adapt CBTM to work under TWC rules, since it is CSX's intention to discontinue use of DTC.
When this development is complete, CSX will begin conducting field tests on its Spartanburg and Blue Ridge Subdivisions. Testing on the Blue Ridge Subdivision will mark the first application of the functionality allowing CBTM to be used within CTC-controlled territory.
BNSF deploys ETMS
BNSF's ETMS is a safety overlay that enforces movement authorities and speed restrictions, monitors point position, and interfaces with broken rail detection systems. It was designed to migrate to a fail-safe (vital) implementation, if needed, to support stand-alone operations.
Fig 4 shows the ETMS onboard display. In this example, the display is informing the crew that the train is approaching a point which is not aligned for its authority. Furthermore, the system has determined that, in order to avoid overrunning the misaligned point, the train driver has 41 sec to take appropriate action before braking is enforced.
ETMS is compatible with the Remote Control Power Switch and Remote Switch Position Monitoring systems currently being tested on BNSF, as well as BNSF's Train Management & Dispatch System, which was implemented in 2005-06 at BNSF's Network Operations Center in Fort Worth.
BNSF's initial testing of ETMS on its Beardstown Subdivision took place on territory under both TWC and CTC. Additional testing is scheduled this year on two higher-density CTC lines, the Fort Worth and Red Rock Subdivisions. This will allow BNSF to test interoperability with other railroads, as both subdivisions also host Amtrak and UP trains.
ITCS in service with Amtrak
Development of ITCS began in 1995 to support higher-speed passenger train operation intermixed with freight train traffic. With funding and support from FRA, Michigan Department of Transportation, Amtrak, and GE Transportation Global Signaling (formerly Harmon Industries), ITCS is in revenue service on 72 km of Amtrak-owned track in Michigan between Kalamazoo and New Buffalo, where 153 km/h is now permitted.
Amtrak is currently awaiting FRA approval to cut-in a further 34 km where ITCS is still officially in test mode, bringing the operational route length to 106 km. The next goal is to lift the permissible maximum speed to 177 km/h along the entire 106 km section.
GE has also developed a stand-alone variant of ITCS that does not require lineside signalling infrastructure, which has been implemented on the 1 100 km Golmud - Lhasa line in China.
ITCS is a radio-based extension of a conventional cab signalling system. It is designed as a vital system integrated with existing signalling, providing enforcement of signal authorities plus permanent and temporary speed restrictions. It uses a network of lineside servers located at each siding (Fig 5). These communicate by radio in a peer-to-peer mode with lineside devices, including points, signals, and grade crossings. Each server monitors the health and status of the lineside devices and provides information that is used to enforce speed compliance by the trains.
For example, a signal displaying a Stop indication would cause the ITCS to issue a target speed of 0 km/h to the onboard display, along with the amount of time the driver has to comply before an enforcement brake application. In Fig 6 the time to penalty is 25 sec.
A feature unique to ITCS is advance crossing activation, which is key to supporting higher-speed passenger operations without requiring new or extended level crossing control circuits. When a train approaches a road crossing, ITCS checks the health of the crossing hardware. If it functioning properly and the train has no other restrictions preventing it from running at 177 km/h, the ICTS will activate the crossing warning devices in time to allow the driver to maintain this speed.
However, if the ITCS system determines that the crossing warning devices are not functioning properly, the onboard display will instruct the train crew to slow to 127 km/h, so that the regulated 20 sec warning provided by the approach detector circuits will not be violated.
ITCS testing began in October 1996. The software is currently undergoing verification and validation that should be completed this autumn. Results will be used to request permission from FRA to increase passenger train speed limits on the route to 177 km/h.
North American Joint PTC
The Najptc project is developing an interoperable, vital PTC system that can be deployed in a stand-alone or integrated configuration. The TTCI-led project is funded by FRA through the Railroad Research Foundation, along with internal funding by Lockheed Martin, the system developer and integrator. Past project funding has also been provided by the Association of American Railroads and Illinois Department of Transportation.
Najptc will provide warning and enforcement of movement authorities and speed restrictions, remote control of points from locomotives, and remote monitoring of train location and movements.
As a whole, Najptc's modular implementation provides flexibility for tailoring to near-term needs with maximum re-use in long-term applications. In addition to improving safety, its emphasis is to increase railroad capacity, average speed, productivity and efficiency while reducing cost as compared with conventional systems.
Najptc is an office-centric vital PTC system. The architecture allows for minimal dependency on or elimination of costly lineside equipment, and provides the same fundamental architecture for all territory types, whether signalled or not. It is intended to permit moving block and centralised conflict checking of all authorities, and has the infrastructure to allow for the voiceless/paperless communication of authorities and restrictions.
Within the locomotive segment, Najptc uses a multi-sensor Location Determination System that relies on the Differential Global Positioning System, tachometer, gyro, accelerometers, track databases and sensor fusion/map-matching algorithms to achieve accurate positioning. This provides highly-dependable track discrimination and dead reckoning through GPS blockages or outages, along with fault detection and superior accuracy.
Fig 7 shows Najptc's onboard display that includes train location, mandatory directives, route profile information, speed and enforcement warnings. Whilst early Najptc testing was performed on UP's Mazonia - Springfield line in Illinois, future testing will take place at Pueblo, where TTCI will prove the system in a controlled environment without interference to or from revenue trains.
Optimized Train Control
Finally, Norfolk Southern's PTC, designed by Lockheed Martin, is known as Optimized Train Control. OTC is designed to be a stand-alone system, but will initially be integrated with existing systems until the necessary regulatory approvals are received. In its Phase I design, OTC provides train location tracking and the monitoring of manual point position. In Phase II it will feature an onboard display, electronic movement authority delivery and enforcement, and speed enforcement.
Fig 8 shows the onboard display for the Phase II design. This will show movement authorities, speed targets, and route profiles, along with other information to the train crew.
OTC ties in with NS's next-generation CAD system, known as Unified Train Control System, which provides real-time advanced movement planning over the NS network. It is also designed to provide OTC with pacing cues for the train driver, which can bring about benefits including reduced congestion, savings in fuel costs, and improved service reliability. NS is integrating NYAB's Leader system with OTC, and will continue testing OTC between Columbia and Charleston, South Carolina, on MBS territory.
- Fig 1. System architecture for a stand-alone CBTC system with centralised safety logic
- Fig 2. System architecture and operating principles for an overlay CBTC system with track-circuit-based safety logic. In some cases, point and signal status information may also be forwarded to the office server
- Fig 3. The locomotive display screen for CSXT's CBTM equipment is installed to the left of the driver's train management display
- Fig 4. The on-board display for BNSF's ETMS gives the driver information about track layout, point positions and movement authorities as well as speed limits and braking instructions
- Fig 5. Amtrak's ITCS uses a series of lineside servers communicating by radio with points signals and level crossings as well as the trains
- Fig 6. Unlike the graphic presentation used by other systems, the ITCS on-board display provides numerical data on actual and permitted speed, target speed and distance, and a short description of the next target type expected
- Fig 7. The NAJPTC on-board display includes train location, route profile information and mandatory directives as well as speed and enforcement warnings. The on-board display being developed for for Phase II of Norfolk Southern's OTC (Fig 8, below), will use a very similar graphical format
Le contrôle-commande des trains par transmission de données aux Etats-Unis entre en service
Les efforts pour mettre au point un système de transmission de données efficace et abordable afin de créer le Positive Train Control - généralement connu en dehors de l'Amérique du nord sous le nom d'Automatic Train Protection - ont fait leur chemin depuis les années 1980. Un cap important a été franchi en décembre 2006 lorsque la Federal Railway Administration a homologué l'Electronic Train Management System de Wabtec sur le BNSF, tandis que le contrôle-commande par transmission de données a amélioré significativement sa progression, avec de nombreuses applications en cours à travers les USA. L'adoption sur une grande échelle offre la possibilité d'augmenter la sécurité, d'abaisser les coûts, d'améliorer le service et d'accroître la capacité du réseau
Die Kommunikations-basierter Zugsicherung wird in den Vereinigten Staaten eingeführt
Die Bemühungen zur Entwicklung von brauchbaren und bezahlbaren Kommunikations-basierten Systemen zu Positive Train Control-Systemen - ausserhalb von Nordamerika als Automatische Zugsicherung bezeichnet - liefen seit der Mitte der 80er-Jahre des 20 Jahrhunderts. Ein wichtiger Meilenstein wurde im Dezember 2006 erreicht, als die zuständige Behörde (Federal Railroad Administration) die Installation von Wabtec's Electronic Train Management System bei BNSF autorisierte. Kommunikations-basierte Zugsicherung hat zudem signifikanten Aufschwung genommen, mit einer grossen Anzahl Anwendungen, welche USA-weit entwickelt werden. Die Einführung in grossem Rahmen hat das Potenzial zur Verbesserung der Sicherheit, Verringerung der Betriebskosten, Verbesserung der Leistungen und Steigerung der Netz-Kapazität
El control de trenes basado en comunicación de datos entra en servicio en EEUU
Desde principios de la década de los 80, se han sucedido los esfuerzos para desarrollar sistemas efectivos y asequibles basados en la comunicación de datos que ofrezcan el Positive Train Control, conocido fuera de Norteamérica como protección automática de trenes o ATP. El mayor hito se logró en diciembre de 2006 cuando la Federal Railroad Administration aprobó la instalación del Electronic Train Management System de Wabtec en BNSF. Además, el control de trenes basado en comunicación de datos ha alcanzado su mejor momento gracias a las numerosas aplicaciones recientemente desarrolladas en EEUU. Su adopción a gran escala permite mejorar la seguridad, reducir los gastos operativos, mejorar el servicio y aumentar la capacidad de la red