OVER THE NEXT 11 years, five of London Underground’s lines are to be resignalled by the Metronet consortium which has acquired the BCV and SSL infrastructure companies as part of the Public-Private Partnership. Work will start with the deep-level Victoria line, followed by the complex network of sub-surface lines - Metropolitan, Hammersmith & City, District and Circle. Total cost of the resignalling programme is put at more than £850m.
Within the Metronet consortium, which took control of Infraco BCV and Infraco SSL on April 4 (RG 5.03 p252), Bombardier Transportation Total Transit Systems is responsible for electrical and mechanical works. Bombardier will be supplying the trains itself, but has appointed Westinghouse Rail Systems as its exclusive supplier for signalling and control systems.
The Victoria line was the world’s first mass transit line equipped with automatic driving when it opened in 1968. That original system was supplied by Westinghouse, and formed the basis for the subsequent installation of Automatic Train Operation on a number of metros around the world.
Not only must the Victoria line remain in service during the modernisation work, the demanding specifications in the PPP contracts require a steady improvement in performance at the same time. As a result, Westinghouse is combining off-the-shelf hardware in an incremental approach.
Work is due to be completed in 2012, but the first of the new trains will start running in 2007. These trains will be equipped from the outset with the new train control equipment, but they will have to operate in mixed traffic with the older trains using the original ATO.
Thus Westinghouse has adopted an overlay strategy, linking the new equipment into the existing signalling as it is installed. Vital safety will be maintained by the original interlockings, and the existing rolling stock will run under the current ATP and ATO. As the new trains are phased in they will run using the new ATO and ATP system, but still under the protection of the existing signalling. Only when the last of the old trains is withdrawn will the signalling be cut over and the modernisation programme completed.
Vital safety under the new system will be provided by seven Westrace dual-processor interlockings. Westrace is already in service in Spain, Australia, Malaysia and other countries as well as on London Underground’s Central line and the Jubilee Line Extension to Stratford. The interlocking modules will be installed and wired up to ’listen’ to the existing interlockings and the outputs from track circuits during the overlay period. When the new Automatic Train Supervision equipment is commissioned, it will take over responsibility for setting routes through the line’s existing interlocking machines.
In effect, continuity of service on the Victoria line will be maintained during modernisation by dual fitting the track. On the Sub-Surface lines, which form a much larger network including many flat junctions, the existing trains are manually driven. Trip cocks are provided to give protection against over-running red signals, so it will be possible to dual fit the trains. This will allow the resignalling work to be staged by geographical areas.
Lineside equipment
Also known as Distance To Go-Radio, TBS100 is Westinghouse’s latest platform for ATP and ATO. It is also proven technology, being fitted on the Jubilee Line Extension and the Madrid metro (RG 10.01 p689) and currently being installed on Line 13 in Beijing. A major advantage of DTG-R is that it can be overlaid, tested and commissioned on the Victoria line while the existing trains keep running.
Routing and regulating of trains will be the responsibility of the Westinghouse-supplied Automatic Train Supervision sub-system in the control centre. Using a central timetable database, ATS sets routes via Local Site Computers. Each LSC communicates with the ATO equipment and Westrace interlockings in its area. It also exchanges data with adjacent LSCs.
Train running information is returned to the ATS, where it is compared with the timetable for regulation purposes. Should manual intervention be necessary, for example to increase service frequency to provide extra capacity as people leave an event, the timetable is edited on-screen and ATS implements the changes automatically.
Also linked to the LSC is the Platform ATO Communicator which provides two-way track-to-train communication in the station area. The PAC has two sets of aerials between the rails at each platform, which exchange signals with an ATO antenna beneath each train cab.
When a train stops at a platform, it establishes communication with the PAC. Information from the train is passed to the LSC, which in addition to forwarding the message to the Control Centre also provides information to the Station Management System. As well as driving the passenger information displays on the platform, SMS provides a count-down clock for platform staff. This facility should enhance train regulation under ATS.
Information on departure time, as determined by the ATS timetable, is transmitted to each train by the PAC. Editing the timetable may result in the ATO being instructed to depart early or late from a platform. Coasting information may also be passed over this link, as may station skip instructions. Text messages may also be transmitted to drivers or for display on the information screens in the train.
On-train functions
On board, the Westinghouse system uses entirely separate ATO and ATP modules. The ATO ’drives’ the train on the basis of the route and run data contained within its memory and signalling information received from the ATP. The ATP monitors the speed and intervenes if necessary.
ATO is programmed to drive the train as fast as possible for as far as possible, whilst keeping within the speed profile and its authorised safe distance ahead. Using the route data in its memory, such as gradients and speed restrictions, updated position information and the train’s braking characteristics, the ATO calculates the braking curve needed to respect a speed restriction or station stop and brakes accordingly. At the next station the ATO brings the train to a halt with the receiver over the PAC aerial.
Information on the route set and line occupancy ahead, needed to determine the movement authority, is taken from the Westrace interlocking by the Fixed Block Processor. The processed data is passed to a Fixed Communications Unit which continually broadcasts the information to the trains through a leaky feeder cable alongside the track. With this radio system, all trains in an area receive all the information. The ATP on each train makes the individual decision on the relevance of the message to its particular status.
Take, for an example, a junction where the turnout has a speed restriction. The speed information for both routes is held in the on-train database. If the FBP transmits that the diverging route is set, the ATO on an approaching train calculates the maximum speed and drives accordingly.
Data transmission is two-way, and each train can report its location to the Westrace interlocking via the FBP. This may seem a duplication of detection, given that the line is fully track-circuited. However, it means that the interlocking is notified as soon as a train has cleared a junction and can thus reset the route earlier. While the time saving is small, it offers a further contribution to more efficient regulation.
Such refinement depends on accurate location of the train between stations, a fundamental requirement as the ATO and ATP both operate on the basis of the distance to go to the next station, change in speed profile, or occupied track circuit ahead. To ensure the necessary accuracy, Absolute Position Reference transponders are installed at intervals along the track, as well as at stations. A degree of redundancy is provided through a typical spacing of 150m.
Between transponders, the train continuously determines its location using two axle-mounted tachometers plus a Doppler radar. These provide speed signals which are integrated by the ATO and ATP to give distance travelled. It is accepted that there will be variations between the sensors, for example as a result of different wheel diameters. Thus all the outputs are compared, allowing for the accuracy tolerance. The true speed is taken to be that at which all the tolerance bands overlap.
Station stops are also simplified. The original auto-driver on the Victoria line has a hard-wired braking rate and updates its location on the braking curve during the run in. With the new system, the on-board map of the next stop and the continuous updating of position using the APR plus on-board distance measurement will enable more accurate stopping. In addition, the PAC aerials are used to give the ATO a position signal accurate to within 1·5m as it comes up to the stopping point. The loop aerials incorporate transpositions at regular intervals and this spacing is used to ’fine tune’ the final braking to an accurate stop.
Victoria line heads Metronet renewal
INTRO: Design work is well underway for installation of radio-based automatic train control on London’s Victoria line, as part of an £850m investment funded through the Public-Private Partnership. Roger Ford looks at the technology
OVER THE NEXT 11 years, five of London Underground’s lines are to be resignalled by the Metronet consortium which has acquired the BCV and SSL infrastructure companies as part of the Public-Private Partnership. Work will start with the deep-level Victoria line, followed by the complex network of sub-surface lines - Metropolitan, Hammersmith & City, District and Circle. Total cost of the resignalling programme is put at more than £850m.
Within the Metronet consortium, which took control of Infraco BCV and Infraco SSL on April 4 (RG 5.03 p252), Bombardier Transportation Total Transit Systems is responsible for electrical and mechanical works. Bombardier will be supplying the trains itself, but has appointed Westinghouse Rail Systems as its exclusive supplier for signalling and control systems.
The Victoria line was the world’s first mass transit line equipped with automatic driving when it opened in 1968. That original system was supplied by Westinghouse, and formed the basis for the subsequent installation of Automatic Train Operation on a number of metros around the world.
Not only must the Victoria line remain in service during the modernisation work, the demanding specifications in the PPP contracts require a steady improvement in performance at the same time. As a result, Westinghouse is combining off-the-shelf hardware in an incremental approach.
Work is due to be completed in 2012, but the first of the new trains will start running in 2007. These trains will be equipped from the outset with the new train control equipment, but they will have to operate in mixed traffic with the older trains using the original ATO.
Thus Westinghouse has adopted an overlay strategy, linking the new equipment into the existing signalling as it is installed. Vital safety will be maintained by the original interlockings, and the existing rolling stock will run under the current ATP and ATO. As the new trains are phased in they will run using the new ATO and ATP system, but still under the protection of the existing signalling. Only when the last of the old trains is withdrawn will the signalling be cut over and the modernisation programme completed.
Vital safety under the new system will be provided by seven Westrace dual-processor interlockings. Westrace is already in service in Spain, Australia, Malaysia and other countries as well as on London Underground’s Central line and the Jubilee Line Extension to Stratford. The interlocking modules will be installed and wired up to ’listen’ to the existing interlockings and the outputs from track circuits during the overlay period. When the new Automatic Train Supervision equipment is commissioned, it will take over responsibility for setting routes through the line’s existing interlocking machines.
In effect, continuity of service on the Victoria line will be maintained during modernisation by dual fitting the track. On the Sub-Surface lines, which form a much larger network including many flat junctions, the existing trains are manually driven. Trip cocks are provided to give protection against over-running red signals, so it will be possible to dual fit the trains. This will allow the resignalling work to be staged by geographical areas.
Lineside equipment
Also known as Distance To Go-Radio, TBS100 is Westinghouse’s latest platform for ATP and ATO. It is also proven technology, being fitted on the Jubilee Line Extension and the Madrid metro (RG 10.01 p689) and currently being installed on Line 13 in Beijing. A major advantage of DTG-R is that it can be overlaid, tested and commissioned on the Victoria line while the existing trains keep running.
Routing and regulating of trains will be the responsibility of the Westinghouse-supplied Automatic Train Supervision sub-system in the control centre. Using a central timetable database, ATS sets routes via Local Site Computers. Each LSC communicates with the ATO equipment and Westrace interlockings in its area. It also exchanges data with adjacent LSCs.
Train running information is returned to the ATS, where it is compared with the timetable for regulation purposes. Should manual intervention be necessary, for example to increase service frequency to provide extra capacity as people leave an event, the timetable is edited on-screen and ATS implements the changes automatically.
Also linked to the LSC is the Platform ATO Communicator which provides two-way track-to-train communication in the station area. The PAC has two sets of aerials between the rails at each platform, which exchange signals with an ATO antenna beneath each train cab.
When a train stops at a platform, it establishes communication with the PAC. Information from the train is passed to the LSC, which in addition to forwarding the message to the Control Centre also provides information to the Station Management System. As well as driving the passenger information displays on the platform, SMS provides a count-down clock for platform staff. This facility should enhance train regulation under ATS.
Information on departure time, as determined by the ATS timetable, is transmitted to each train by the PAC. Editing the timetable may result in the ATO being instructed to depart early or late from a platform. Coasting information may also be passed over this link, as may station skip instructions. Text messages may also be transmitted to drivers or for display on the information screens in the train.
On-train functions
On board, the Westinghouse system uses entirely separate ATO and ATP modules. The ATO ’drives’ the train on the basis of the route and run data contained within its memory and signalling information received from the ATP. The ATP monitors the speed and intervenes if necessary.
ATO is programmed to drive the train as fast as possible for as far as possible, whilst keeping within the speed profile and its authorised safe distance ahead. Using the route data in its memory, such as gradients and speed restrictions, updated position information and the train’s braking characteristics, the ATO calculates the braking curve needed to respect a speed restriction or station stop and brakes accordingly. At the next station the ATO brings the train to a halt with the receiver over the PAC aerial.
Information on the route set and line occupancy ahead, needed to determine the movement authority, is taken from the Westrace interlocking by the Fixed Block Processor. The processed data is passed to a Fixed Communications Unit which continually broadcasts the information to the trains through a leaky feeder cable alongside the track. With this radio system, all trains in an area receive all the information. The ATP on each train makes the individual decision on the relevance of the message to its particular status.
Take, for an example, a junction where the turnout has a speed restriction. The speed information for both routes is held in the on-train database. If the FBP transmits that the diverging route is set, the ATO on an approaching train calculates the maximum speed and drives accordingly.
Data transmission is two-way, and each train can report its location to the Westrace interlocking via the FBP. This may seem a duplication of detection, given that the line is fully track-circuited. However, it means that the interlocking is notified as soon as a train has cleared a junction and can thus reset the route earlier. While the time saving is small, it offers a further contribution to more efficient regulation.
Such refinement depends on accurate location of the train between stations, a fundamental requirement as the ATO and ATP both operate on the basis of the distance to go to the next station, change in speed profile, or occupied track circuit ahead. To ensure the necessary accuracy, Absolute Position Reference transponders are installed at intervals along the track, as well as at stations. A degree of redundancy is provided through a typical spacing of 150m.
Between transponders, the train continuously determines its location using two axle-mounted tachometers plus a Doppler radar. These provide speed signals which are integrated by the ATO and ATP to give distance travelled. It is accepted that there will be variations between the sensors, for example as a result of different wheel diameters. Thus all the outputs are compared, allowing for the accuracy tolerance. The true speed is taken to be that at which all the tolerance bands overlap.
Station stops are also simplified. The original auto-driver on the Victoria line has a hard-wired braking rate and updates its location on the braking curve during the run in. With the new system, the on-board map of the next stop and the continuous updating of position using the APR plus on-board distance measurement will enable more accurate stopping. In addition, the PAC aerials are used to give the ATO a position signal accurate to within 1·5m as it comes up to the stopping point. The loop aerials incorporate transpositions at regular intervals and this spacing is used to ’fine tune’ the final braking to an accurate stop.
Victoria line resignalling
Westcad control centre
Seven Westrace interlockings
Replacement signal heads, track circuits, point machines and ancillary equipment
TBS 100 Distance to Go-Radio ATP (to be fitted to new trains)
TBS 100 Automatic Train Operation (to be fitted to new trains)
TABLE: Acronym list
APR Absolute Position Reference
ATO Automatic Train Operation
ATP Automatic Train Protection
ATS Automatic Train Supervision
DTG-R Distance To Go-Radio
FBP Fixed Block Processor
FCU Fixed Communications Unit
LSC Local Site Computer
PAC Platform ATO Communicator
SMS Station Management System
CAPTION: RIGHT: Development work underway at the Westinghouse Rail Systems offices in Chippenham
BELOW: Schematic diagram showing the final Westrace-based control system (left) and the intermediate overlay option (right)
