Home: October - November 2007 › Signalling technology for today's railways
Signalling technology for today's railways
01/11/2007 | Channel:
Products & Services, Business Improvement, Infrastructure
Westinghouse is developng signalling solutions for the safety critical rail environment
In a safety critical environment, the development and introduction of new technology must be managed at a pace that meets both regulatory and operational needs, as well as satisfying a business’s commercial requirements for continuous improvement, market and product development.
This environment and approach is particularly evident in the control of the world’s railways, an industry that quite rightly places exceptionally high demands on operational safety, and features rigorous and demanding approval processes. Suppliers to the industry are completely committed to this approach, placing safety firmly at the top of their agenda, and using techniques familiar to those in other safety critical industries, such as aerospace, defence and nuclear power.
Westinghouse Rail Systems Limited (WRSL), part of the worldwide Invensy Group, can trace its roots to the beginning of signalling technology over 140 years ago, and is today a leader in advanced integrated signalling and control solutions for mainline and mass transit railways. In this article, Mark Glover, one of the company’s sales and marketing managers, looks at the development of signalling systems, from the original patent for the interlocking of points and signals, filed by John Saxby in 1856,
through to the complex electronic technology that provides the combination of performance and safety demanded by today’s passengers and railway authorities.
First a brief history. The development of an interlocking system – originally a mechanical system that linked the operation of points and signals in such a way as to prevent trains being routed in a dangerous manner – was truly a pioneering event in rail history, and Saxby’s work was a major breakthrough in the safe operation of railways throughout the world.
In 1860 Saxby joined forces with John Farmer to form a company dedicated to producing railway signalling equipment. Development was rapid, and Saxby & Farmer were joined in the field by a number of other companies. Amalgamation followed swiftly, as the companies produced improved designs of signals, point mechanisms and interlockings to meet the gathering pace of investment in mainline and mass transit railways, throughout the end of the 19th and beginning of the 20th centuries.
Major innovations saw the introduction of Colour Light Signalling, electrically operated lever frames, and as early as the 1930s, complex forms of cab signalling – the forerunner of modern Automatic Train Protection (ATP) systems. Having become part of the Westinghouse group in the early 1900s, the company had access to major technological advances from other Westinghouse companies. This led to one of the first practical implementations of rectifier technology in the UK, a metal rectifier system being used to feed a track circuit at London Paddington station as early as 1925. Other pioneering advances in technology included early remote control systems and sophisticated train identification.
On the mass transit side of the industry, Westinghouse continued its involvement with the rapidly developing London Underground network, culminating in the 1960s with the first trials of fully automated trains being successfully carried out on what was to become the Central Line, part of the development of the groundbreaking system implemented on the Victoria Line in 1968.
The industry saw a period of rapid change after the Second World War, with larger and larger systems being implemented. For example in 1975, what was then the world’s largest geographical relay interlocking was commissioned at London Bridge – with some 13,000 relays providing the processing and interlocking capability. In 1985 a joint development by British Rail, GEC (now Alstom) and Westinghouse saw the first Solid State Interlocking (SSI) installed at Leamington Spa – SSI is now at the heart of the UK railway signalling network.
The inescapable move of the engineering industry towards processor-based technology, saw signalling move rapidly in the 1990s from SSI to more modern processor-based technology such as WESTRACE - one of Westinghouse Rail Systems’ current product ranges - and more recently, to WESTLOCK, an industry–leading, step advance in capacity.
WESTRACE is now applied in well over 1000 locations worldwide, by WRSL and its sister companies Westinghouse Rail Systems Australia, Spanish company Dimetronic Signal, and Safetran Systems Corporation in the USA. A highly flexible system, WESTRACE is a range of hardware modules which can be programmed using ladder logic to deliver almost any vital functionality, in a standalone or networked architecture, to provide SIL4 interlocking, ATP or other control capability. WESTRACE can also provide level crossing control or safe data transmission for centralised traffic control systems, and the latest version is also capable of carrying out large amounts of non-vital processing in parallel with its safety processing.
New modules are regularly introduced to exploit latest advances. For example MoviolaW software displays track circuits, points, signals and other equipment on a mimic panel-style screen, clearly showing the interlocking status and allowing replays of critical events – allowing for rapid problem solving either on-site or remotely. New hardware has been developed to provide more and more processing capability, whilst still maintaining the availability and safety targets set by the CENELEC standards.
Arguably the most significant development of electronic interlocking technology in 25 years, WESTLOCK is the company’s most recent technical innovation – providing fully retro-compatible processing in an advanced and powerful form. Designed to provide a highly efficient upgrade from SSI, and to provide industryleading levels of performance, WESTLOCK is more compact and significantly faster than previous systems.
Taking a Process Industry PLC as its basis, WESTLOCK has been adapted from inception to fully meet all European standards and to provide SIL4 functionality in a proven and structured manner. More than an SSI replacement, WESTLOCK is a state-of-the-art interlocking system, with high-speed datalink capacity allowing rapid communication with a range of control centre solutions, trackside equipment and the European Train Control System (ETCS). ETCS is at the heart of Europe’s drive for interoperability – the same train being able to drive from Glasgow to Milan whilst being able to use the signalling system of each country that is passed through – and both WESTRACE and WESTLOCK have been designed to allow migration from national systems to ETCS.
WESTLOCK offers rail companies the best of all worlds, a painless evolution from SSI with a dramatic revolution in processing speeds, capacity and efficiency - all with high standards of inherent and proven safety. Whilst interlocking development has progressed enormously, so has the on-board safety technology that affords protection to trains and their occupants – on increasingly overcrowded railways. At the heart of these developments in the late 20th and early 21st century has been the significant improvement in train protection systems.
An example of this latest technology is WESTRAN, WRSL’s mass transit Automatic Train Protection and Automatic Train Operation system. WESTRAN has been developed exclusively for use in communication-based train control applications and is particularly appropriate for high density metros. However, the platform on which WESTRAN is based is the TBS100 vital processing system, which Westinghouse also uses as the heart of its ETCS trackside and train-carried products.
The communication-based nature of WESTRAN is such that the amount of trackside infrastructure required is substantially less than for previous systems, providing significant cost reductions for train operating companies and infrastructure owners.
Although primarily designed as a total solution for new infrastructure projects, WESTRAN is also capable of being overlaid onto existing systems during refurbishment or upgrade programmes, enabling a gradual migration to the system over time with minimal disruption to service. This ability to provide upgrades to new solutions without stopping the running railway is a critical part of Westinghouse’s success, with a number of major references demonstrating both the flexibility of the company’s products, and their highly experienced and capable staff.
One project that is benefiting from much of the most recent technology is the London Underground Public Private Partnership (PPP) upgrade, which has seen Bombardier Transportation, working for Metronet, award Westinghouse one of the largest ever signalling contracts. It is a project that includes many elements of the company’s product range.
The first programme of work covers a 14 year period, to upgrade and refurbish the London Underground Victoria Line, covering the design, supply, installation, testing and commissioning of new signalling and train control equipment.
As well as the provision of WESTRACE interlockings, Westinghouse is supplying its ATP and Automatic Train Operation (ATO) systems in Distance-to-Go Radio (DTG-R) mode, all controlled from the company’s WESTCAD Control Centre. ATO provides automatic driving of trains from point to point without driver intervention, thus permitting the best possible overall performance of the railway.
The ATP system performs the fundamental safety needs of keeping trains a safe distance apart and operating at a safe speed. The trackside system sends train-carried equipment information, which is used to determine if the train is operating within safe limits, or to apply emergency brakes if this is not the case.
Signalling systems such as DTG-R allow trains to travel faster and more closely together, whilst maintaining safety. The technology uses radio transmission which allows the system to be overlaid with distance information relating to other trains on the track, providing more comprehensive data for the computation of braking and acceleration instructions.
The radio transmission also drives the ATO system, giving the train its station stop commands. It also transmits data about the time that the train should stop at the station and tells the train how fast it may proceed to the next station (ATP permitting) giving the ability to monitor and control train performance against timetable.
The Victoria Line project is now well underway and sees the total replacement of signal heads, track circuits, point machines and ancillary equipment, with the first new train planned to be running under ATP, in traffic hours, later this year. When the upgrade is complete in 2013, the frequency of rush hour trains is targeted to increase by 17 per cent and journey times should improve by 16 per cent.
The second element of the PPP contract covers work on the Sub Surface Lines (SSLs), which include the Hammersmith and City, District, Metropolitan and Circle Lines. As with the Victoria Line, the scope of the project includes supplying WESTRACE, ATP (DTG-R), and ATO.
At the heart of the project will be two new state-of-the-art WESTCAD Control Centres, one of which is to control the Northern SSL and one the Southern SSL (but each capable of controlling the other’s area). The SSL upgrade programme is planned to run until 2014, although rail passengers will begin to see the benefits of the upgrade much sooner.
The DTG-R technology will initially be interfaced to existing Interlocking machines through WESTRACE safety processors. This will allow the existing rolling stock to operate under the control of the existing ATP and ATO systems on the Victoria Line. As new trains are introduced, they will work under the new ATO and ATP systems, but still under the overall protection of existing signalling.
Then as new infrastructure equipment is installed, the travelling public will experience
a dramatic increase in the overall reliability and consistency of journey times on both the Victoria Line and SSLs. With the introduction of new rolling stock, the full power of the signalling system will be experienced with the DTG-R system permitting an increase in train frequency whilst enhancing safety.
Systems have certainly come along way from the days of John Saxby in the 19th century. Signalling and train control systems have become more complex and able to manage the world’s railway networks in increasingly reliable and safe operations. But as demands change, so technology must continually evolve – and the next generation of systems are already in development.