INTRO: Recent Transmission-Based Train Control pilot projects and new efforts to set international standards foreshadow the future direction for the next generation of train control technology. But where is it all going and why is it taking so long?
BYLINE: Tom Sullivan
Transportation Systems Design Inc*
CALL IT WHAT you will, Transmission-Based Signalling, Communications-Based Train Control, European Train Control System, or Positive Train Control, increasingly the consensus among signalling suppliers and customers alike is that the technology will replace traditional fixed-block signalling. But what is holding back widescale deployment, and will there be a single standard for TBTC?
Fixed-block signalling has ensured safe train operation for well over a century, particularly following the advent of track circuits which detect the presence of trains through the rails. But as rail operators begin to demand more capacity and operational performance under failure conditions, it is becoming clear to many that the fixed-block track circuit technology has reached its limit.
Transmission-Based Train Control in its ultimate configuration is a means to detect and control the position of trains using software in safety-critical computers, which communicate with the trains in real time. While there may be stepping stones on the way that will temporarily make use of track circuits or transponders as location markers (known as a ’balise’ in Europe and a ’tag’ in the USA) the ultimate goal is to eliminate, as much as possible, track circuits and other lineside equipment.
There are various ways to communicate with trains without using track circuits. Both the original LZB moving-block technology, marketed today by Siemens, and its urban descendant Seltrac, developed by Alcatel, use highly reliable inductive loop technology to transfer information between on-board antennae and a simple wire loop running down the track.
Some operators are queasy about the apparent vulnerability of a wire loop, and are seduced by the apparent simplicity of radio frequency links. Most observers agree that RF technology will eventually replace loops, but today it is difficult to ensure the 100% radio coverage that most people believe is essential for reliable operation.
Reliable RF coverage is especially difficult in highly variable subway environments. Adtranz therefore elected to partner with Andrew to develop an RF radio network using leaky coaxial cables for its Flexiblok TBTC. Others believe that free space propagation can be reliable in metro situations, and both Harmon at BART and Kasten Chase at NYCT are out to prove that it can be done.
Early pioneers
Unlike the rapid conversion from steam to diesel and electric traction, widespread acceptance of TBTC has been slow. Several of the early projects have been seriously delayed, and the lack of standards for TBTC is seen by many observers as a serious impediment to widescale acceptance. Understandably, few operators are willing to accept the risk of getting stuck with a proprietary system - especially if there is a risk of it turning out to be a technological orphan.
But for many paradigm pioneers, the benefits of TBTC are worth the price. San Francisco’s Muni Metro is a typical bad-news good-news example. In 1992 Muni agreed with Alcatel that it should take three years to install Seltrac TBTC. But nearly seven years later the project is still not finished. There are many reasons for the delay, but Muni’s Patty DeVlieg says that both sides seriously underestimated the effort it takes for an operating railway to become comfortable with a fundamentally different way of running its trains.
Prior to the introduction of TBTC, Muni was unable to handle more than 23 trains/h through its downtown subway under Market Street. Today, with Seltrac in operation, Muni is running half as many again, and when fully deployed, TBTC is expected to deliver an impressive 48 trains/h.
Such significant performance improvements are tempting to operators, because construction alternatives to accomplish the same objective are normally much more expensive. Several operators have already opted for Seltrac, including London’s Docklands Light Railway, and most recently, the 30 km West Rail Phase I in Hong Kong. KCRC plans to transport over 500000 passengers/day each way using 130 km/h trains at peak headways of just 96sec.
Thus, despite slow initial acceptance, TBTC technology continues to win supporters. Other suppliers are now marketing and installing their own proprietary versions.
For example, Adtranz is currently installing Flexiblok for the new peoplemover at San Francisco International Airport and on the Market-Frankford metro line of South Eastern Pennsylvania Transit Authority. Paris metro Line 14, the driverless Météor, uses the latest version of Matra Transport International’s TBTC to achieve 85sec headways. And also in San Francisco, BART is using Harmon Industries’ EPLRS advanced radio network, developed originally by Hughes Aircraft Corp for the US military at a cost of over $500m.
Despite this upturn in interest, most operators appear to have chosen to sit on the sidelines and await the outcome of new initiatives which could see the emergence of some common standards.
Towards common standards
In the US urban market, most agree that the MTA New York City Transit Canarsie line resignalling is the project to watch. With 6000 cars and nearly 1200 km of signalled track, the NYCT subway network has enough critical mass to set the de facto standard for urban TBTC applications. Similarly, two railroad-led Positive Train Control initiatives are beginning to converge on a common core technology, which is likely to result in a common PTC/TBTC standard for North America’s main line railroads.
In Europe, the three-level ETCS programme appears to be the hands-down favourite for the main line networks. The urban situation remains fuzzy, but the involvement of major international signalling firms Alcatel, Alstom, and Siemens/Matra in the NYCT programme may see the adoption of similar standards around the world.
Most signalling suppliers agree that the world market for TBTC is not big enough to support more than a few (incompatible) standards. But it also appears that the differences between the European mixed-traffic environment and the freight-dominated North American requirements make it unlikely that a single worldwide TBTC standard will emerge.
Surprisingly, the three firms shortlisted for the NYCT trial installation (Alcatel, Alstom, and a joint venture consisting of Matra/Siemens, Union Switch & Signal and Telephonics) all independently selected the same Kasten Chase radio network. RailPath was designed from the ground up for the harsh metro environment. Operating at 2·4GHz in the unlicensed ISM band, it is an Internet Protocol based radio network that uses a hybrid direct-sequence/frequency-hopping spread-spectrum radio.
Because of the scale of future NYCT procurement running into billions of dollars, RailPath radio may become the de facto TBTC radio standard, at least in the USA. Co-operation among suppliers is key. Kasten Chase’s Herman Chang says ’what has been particularly gratifying has been the strong teamwork we have been able to build with all three companies during these crucial TBTC tests at NYCT.’
Another promising standardisation effort in the urban sector is being funded by the US Transportation Research Board, with support from the Federal Transit Administration. Using the Institute of Electrical & Electronics Engineers as its standards body, this effort has significant support from signalling suppliers and urban rail operators around the world.
The IEEE Rail Transit Vehicle Interface Standards Committee has reached consensus on two key TBTC-related standards. IEEE 1473 ’Communications Protocols On Board Trains’ is a completed standard, and ’Performance & Functional Specifications for Communications-Based Train Control’ is in final draft form and should be published shortly.
IEEE 1473 is of immediate interest to car builders and those who write specifications for them. Embracing two existing standards, TCN and LonWorks, it has the potential to revolutionize the design, supply and integration of subsystems for urban rail vehicles. Already, NYC Transit, which needs to replace an average of 200 subway cars per year, now mandates LonWorks (IEEE 1473-L).
Heavy rail standards
For the US freight railroads, the same LonWorks protocol specified in IEEE 1473 was adopted as a standard by the American Association of Railroads for electronically-controlled pneumatic (ECP) brakes (RG 2.98 p95). Potentially, around 1·5 million freight wagons in North America could be wired with serial train lines controlled by LonWorks.
In the longer term, this new standard serial trainline potentially makes feasible remote monitoring and control of systems such as refrigeration and hot bearing detectors with information transferred to the lead locomotive. But getting the information off the train and into the control centre is dependent upon other standards efforts associated with digital train radio.
In Europe and most of the world, GSM is a well-established standard for wireless communication using digital cellular phones. Unfortunately GSM has a relatively small market share in the USA, where several incompatible digital cellular phone technologies dominate the industry.
Thus it is Europe that is leading the development of GSM-R, a new GSM network with uplink and downlink frequencies dedicated exclusively for rail applications. After much discussion, 32 European railway operators have signed up to the UIC specifications for GSM-R, and the first trial installations are under way. Sweden’s Banverket is the first to adopt GSM-R for its entire national radio network, with Siemens equipment replacing four existing systems as it comes on stream over the next three years.
But while GSM-R is likely to be the standard wireless communications technology for trains in Europe (and probably much of the world), development is behind schedule. Several ETCS pilot projects may soon be adversely affected by its late deployment. In addition, some suppliers are waiting until it becomes clear that GSM-R will be standardised, or at least, more fully deployed.
There is some chance that GSM-R will be successful in North America too, especially if the US signal industry and railroads cannot agree common standards for a safe, interoperable and cost-effective TBTC under the Positive Train Control initiative.
PTC is the second major attempt by the US railroads to build a radio-based train control system. While a few Advanced Train Control System pilot programs were demonstrated in the mid-1980s, ATCS was effectively stillborn. By the mid-1990s it was widely seen as a victim of excessive optimism, and reluctance by the railroads to make the required major infrastructure investment in a wayside radio and communications network.
But some good initial work was done by the designers of ATCS. For example, the original communications protocol survives today and suppliers such as Harmon and Safetran have interoperable products that communicate over this common protocol. Although safety is a key objective, the US railroads believe that without interoperability, cost-effective PTC systems will be impossible. And without cost-effective systems, they will not be widely deployed.
To address this issue, the Eastern PTC programme headed by CSX and Norfolk Southern adopted LonWorks as its on-board locomotive protocol. The North American PTC programme, the other major trial involving UP, BNSF and GE Harris, is also likely to adopt LonWorks. By so doing it has leveraged some important architectural concepts and standards processes, such as LonMark Profiles, which should help to ensure cost-effective interoperable systems.
Looking ahead
It is always dangerous to predict the future with advanced technology. But it is a pretty safe bet that both urban and main line rail operators will increasingly demand, and acquire, interoperable TBTC systems.
For the European railways ETCS and GSM-R appear to have a strong standards lead that cannot be overtaken. But in the US main line market, where GSM is not well established, another path is likely to be blazed. While this will probably include LonWorks, the rest of the final architecture is still unclear.
In the North American urban market, a TBTC standard is likely to emerge from the NYCT development programme. The sheer size of the project and the active support of new IEEE standards based on LonWorks makes this a fairly safe bet.
* Tom Sullivan was Director, New Technology Train Control, at New York City Transit before joining Parsons Brinckerhoff. He now runs Transportation Systems Design Inc, providing consultancy services on TBTC. Links to additional information on many projects described in this article are available from his web site www.tsd.org
CAPTION: One of the first North American Class Is to adopt Positive Train Control is the Alaska Railroad, where GE Harris is installing its PTS equipment developed with UP and BNSF alongside a computerised dispatching system over the next three years Photo: GE Harris
CAPTION: Seltrac transmission-based signalling has increased the capacity of San Francisco Municipal Railway’s Market Street light rail subway from 23 to 35 trains/h each way, with an eventual target of 48
CAPTION: If only because of its scale, the New York City Transit TBTC programme is likely to set a de facto standard for the North American metro industry. The three shortlisted suppliers completed their field tests on July 16, and the announcement of a preferred bidder is expected shortly
CAPTION: All three consortia shortlisted by NYCT selected RailPath radio technology from Kasten Chase. The RF routers (top) are mounted in a NEMA standard lineside enclosure with optical fibre links. Lineside and on-train interface units (above) translate the data messages to and from the internet-protocol format
Operators await TBTC standards
Various pilot projects are already proving the potential of Transmission-Based Train Control, and efforts are under way to set international standards for radio and systems protocols to support the next generation of train control technology. Market conditions and operating requirements suggest that variants will evolve for urban and main line applications in Europe and North America, but Tom Sullivan finds that many operators are holding back on major investment decisions until the future standards are established
Les opérateurs attendent les normes TBTC
Divers projets pilotes montrent déjà les potentialités d’un dispositif d’arrêt automatique à transmission radio (TBTC) et des efforts sont menés pour mettre en place des normes internationales pour la transmission radio et des règles protocolaires des systèmes, afin de préparer la technologie de la future génération des dispositifs d’arrêt. Les conditions du marché et les nécessités de l’exploitation laissent à penser que des variantes évolueront pour application dans les transports urbains et sur les grandes lignes, en Europe et en Amérique du Nord, mais pour Tom Sullivan, beaucoup d’exploitants préfèrent ne pas se lancer dans des investissements importants, en attendant l’élaboration de normes futures
Betreiber warten auf Normen bei Funkgestützten Zugleitsystemen
Eine Reihe von Pilotprojekten zeigen bereits jetzt das in Funkgestützten Zugsleitsystemen steckende Potential auf, und es laufen Bemühungen, internationale Normen für Funk und Systemprotokolle bei der nächsten Generation der Zugleittechnik aufzubauen. Marktbedingungen und betriebliche Ansprüche machen glauben, dass sich Varianten für Anwendungen in städtischer Umgebung und auf Hauptstrecken in Europa und Nordamerika herausbilden werden, aber Tom Sullivan stellt fest, dass Betreiber mit ihren Investitionsentscheiden sehr zurückhaltend sind, bis die künftigen Normen sich etabliert haben.
Los operadores en espera de las normas TBTC
Varios proyectos pilotos ya est
