Westinghouse is applying its most advanced technology, proven in the UK and on overseas metros, as Metronet's Victoria Line resignalling hits the ground running.
After all the debate, political confrontation and negotiations it is time for the London Underground PPP to start delivering. A public rendered sceptical by the privatisation of British Rail will judge the new era, in large part, on how soon the promised investment starts producing results.
As with the mainline railway, the time taken to strike deals with the private sector means that already overdue renewal projects have slipped back further. Thus the two PPP consortia and their suppliers have the double pressure of recovering from this investment hiatus while demonstrating early benefits.
For the public, one criterion of success will be new trains that run reliably to close headways, increasing capacity. And for Metronet, which has acquired the BCV and SSL Infracos, new trains and re-signalling are key components of the long term investment plans.
Within the Metronet consortium Bombardier Transportation – Total Transit Systems (BT-TTS) is responsible for the supply of trains and signalling. Obviously the company will build the trains but, has made Westinghouse the exclusive supplier for signalling and control.
Under two contracts, together worth over £850million, Westinghouse will resignal the Victoria Line and the sub-surface lines – (Metropolitan, Hammersmith & City, District and Circle) over the next 11 years.
Priority goes to the Victoria Line. When its first section opened in 1968 it was the world's first mass transit line with automatic driving using technology supplied by Westinghouse. That first generation Automatic Train Operation (ATO) evolved rapidly as the expertise was exported. But while a number of upgrades have been made to the Victoria Line ATO at subsystem level, complete resignalling is now over-due.
Bombardier and Westinghouse have already worked together on the Central Line. Westinghouse resignalled the line as part of the modernisation which included the new train fleet. This relationship is the basis of the new contracts.
A vital feature of these PPP contracts is that BT-TTS and Westinghouse will be penalised if equipment doesn't perform as advertised – for example, if the signalling can't provide the specified capacity. Hence the use of proven equipment and systems where possible
Westinghouse is using off-the-shelf hardware for all the resignalling. Vital safety will be handled by the Westrace dual processor interlocking already in service on the Central Line resignalling and the Jubilee Line extension as well as the Beijing and Singapore mass transit systems overseas.
Westrace uses diversity in a single processor rather than the parallel processors which formed the basis of the original Solid State Interlocking (SSI) and the new generation Computer Base Interlockings. Approaching 700 interlockings are installed worldwide.
In terms of other Westinghouse contracts , Victoria Line resignalling is smaller than Central Line but similar in size to JLE, the Beijing Metro and an individual Phase of Singapore Mass Transit. It will require seven new interlockings.
Victoria Line ResignallingScope of worksSeven Westrace interlockings TBS 100 Distance to Go – Radio ATP (new trains) TBS 100 Automatic Train Operation (new trains WESTCAD control centre Replacement signal heads, track circuits point machines and ancillary equipment
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Sub-Surface Lines ResignallingScope of works?? Westrace interlockings TBS 100 Distance to Go – Radio ATP (new trains) TBS 100 Automatic Train Operation (new trains Two WESTCAD control centres ( Northern SSL and Southern SSL each able to control both areas) Replacement Replacement signal heads, track circuits point machines and ancillary equipment
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Westrace is an evolving technology. It is now ethernet enabled which means that ATO and ATP commands can be passed to the train over non-vital radio links.
TBS100 is Westinghouse's latest platform for ATP and ATO. It is in service on JLE, the Madrid Metro and is currently being installed on Line 13 in Beijing .
With the need to keep the Victoria Line running, and with improving performance levels,during modernisation the plan is to migrate progressively to the new signalling and control system. One advantage of the Distance To Go-Radio (DTG-R) system being supplied by Westinghouse is that it can be overlaid on the line, tested and commissioned while the existing trains keep running.
Understanding the AcronymsAPR - 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
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To understand the phased introduction, a description of the definitive system is needed first. Readers are warned that this is hard going, but, I hope, worth the effort. You will need this table of acronyms
As in all modern systems the control centre has two functions. There is the primary task of routing and regulating the trains which is handled by the Automatic Train Supervision (ATS) sub-system. In the same room there are desks for the control of power supplies, station communications and similar functions.
Working from a central Timetable Data Base the ATS sets routes via Local Site Computers (LSC). In ‘classic' Underground signalling, the ATS is the equivalent of the electro-mechanical Programme Machines which set routes through junctions according to the timetable, originally stored on punched card rolls.
However, in the 21 st Century the LSC is more than a piano roll player. It communicates with both the ATO system and the Westrace interlockings in its area plus ‘fringe' LSCs.
This train information is sent back to the ATS in the control centre. Normally, the ATS hums away happily, running the service in the timetable. But should staff want to change the service, for example increase evening frequency to provide extra capacity as people leave an event, they simply edit the timetable on screen and ATS implements the change.
Functionally, this is the same as the Central Line ATO and ATS. However, the Victoria Line is a simpler network, requiring little if any of the conflict management needed on the Central. The SSL resignalling will be much more of a challenge.
So, the ATS controls regulation and route setting via the LSC which instructs the Westrace accordingly. The next stage is to bring the trains into the loop.
First, there is the Platform ATO Communicator (PAC). This is connected to two sets of aerials in the four foot at each platform. Mounted beneath each train cab An ATO antenna which receive signals from these aerials
When a train stops at a platform, it establishes communication with the PAC. Train information from the PAC goes to the LSC which in addition to forwarding the information to the Control Centre also provides information to the Station Management System (SMS) which has two functions.
First, it drives the passenger information displays on the platform. But second, it provides a count down clock for platform staff. A similar facility is already in action on the Central Line. If you watch the PIS displays you will see a small square appear. This is the ATS warning platform staff that the train should leave in 8-10 seconds time.
Why are count downs important? Well, remember that the ATS is regulating the service. Thus it is important that the train leaves on time.
In addition to receiving information, the PAC also transmits information to the train on the route ahead and the driving technique necessary to maintain the schedule as determined by the ATS timetable. If the timetable has been edited, the ATO may be instructed to increase or reduce coasting during the run, change the braking rate or skip the next station. The PAC can also transmit text messages to drivers or to the information screens in the train.
Information from the PAC is processed by the on-train ATO equipment which controls traction, braking and doors.
Note at this stage that ATO and ATP are separate functions. As with manual driving, the ATP monitors the train performance determined by the ATO and intervenes if necessary.
So far we have a train which has been given the route ahead, including the speed profile needed to both maintain the schedule and stay within speed restrictions. The LSC has told the Westrace interlocking which route to set.
ATO and ATP know the train's precise position because it will be sitting on top of Absolute Position Reference (APR) transponders – one at each end of the train. An APR reader on the train passes this information to the ATO and the ATP.
There are two readers because the ATO and ATP needs to know where the rear of the train is. For example, when leaving a speed restriction the train cannot accelerate until the rear of the train is clear,
ATO has a simple job. It has to drive the train as fast as it can for as far as it can, while keeping within the speed profile and its authorised safe distance ahead.
As it drives it looks ahead at the route data in its memory. It knows the train's braking characteristic so that as a speed restriction or a stop approaches it starts to brake so that the braking curve achieves the new speed at the start of the restriction.
At the next station the ATO also has to brake to a halt with the ATO receiver over the aerial and the APR readers over the transponders.
To provide protection the ATP also needs to have information on the route set, speed restrictions and track circuits occupied ahead. This information is in the Westrace Interlocking and is prepared for transmission to the trains by the Fixed Block Processor (FPB). The processed data is passed to a Fixed Communications Unit (FCU) which broadcasts the data through the leaky feeder cable alongside the track.
Note a big difference here with classic ATP where transponders or coded track circuits talk to trains individually. With the Westinghouse system, all trains in an area receive all the information and each train makes the decision on how to apply this information to its particular status. In other words, all the clever kit is on the ‘smart' train.
Transmission is two way and the train can transmit its location to the FBP and thus to the Westrace Interlocking. This means that the interlocking knows as soon as a train has cleared a junction and can reset the route earlier.
ATO and ATP is based on distance to go, whether to the next station or the next change in speed profile or the next occupied track circuit. Thus it is essential for the train to know where it is all the time.
APR transponders at stations have already been mentioned. These are also spaced along the line so that a faulty unit does not bring the whole system to a halt. Typically, there will be an APR every 150m.
Between transponders the train keeps track of its location through two axle mounted tachometers plus a Doppler radar. These sensors provide speed signals which are integrated by the ATO and ATP to give distance travelled. Outputs are compared, including a tolerance for accuracy, and the true speed taken as where these bands all overlap .
Thus the train always knows where it is and through the information from the FBP knows the status of the fixed blocks ahead. In addition, its memory also holds the map of the route so that it knows about speed restrictions and gradients.
Using this information the ATO continuously calculates its movement authority – the distance ahead it can run. Note, too, that because ATO and ATP share the same information the ATO is clever enough to calculate a braking curve which just stays within the ATP's intervention curve.
DTG-R pays benefits at junctions. Suppose straight ahead is Block 1 at 1ine speed and the diverging route is Block 2 with a speed restriction. These details are in the on-train equipment's ‘map' of the route. Thus when the FPB transmits the route, the on board kit notes that Block 1 or Block 2 is ahead and drives the train accordingly.
Station stops are also simplified by the ‘smart' train. The original auto-driver on the Victoria line has a hard wired brake rate and updates its place on the braking curve during the run in. With an on board map of the next stop and a train that knows where it is, auto-driving is much simpler.
Thus with an arriving train the PAC aerials tell the ATO its location to within +/-1.5m as it comes up to the stopping point. Note that the loop aerials cross over. These crossing points are called transpositions and their spacing is used to ‘fine tune' braking to an accurate stop.
So that is how the modernised Victoria Line's new trains will start running in 2007, with work completed in 2012. But between now and then the new signalling has to be installed while the existing stock and signalling maintain the service.
Westinghouse will overlay the new system. The Westrace modules will be installed and wired up so that they ‘listen' to the existing interlockings and the outputs from track circuits.
Similarly, when the new ATS system is commissioned it will start setting routes using the existing Westinghouse Model S2 interlocking machines. Westrace has a port which can communicate with the S2 . 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 introduced they will run using their own ATO and ATP but still under the protection of the existing signalling until all the new trains are in service and the lineside kit installed. Then the Westrace interlockings takes over
On Victoria Line, Westinghouse is dual fitting the track. On SSL, which is manually driven, it will be possible to dual fit the trains while signalling is being installed, since ATP is provided by trip cocks. This means that resignalling can be phased over a series of areas.
But operationally SSL is a much more demanding system and while at Chippenham researching this article I was shown some of the computer modelling which is simulating the performance of DTG-R. This has a route diagramme on which ‘trains' run with their ATP and ATO speeds and braking curves superimposed.
Such modelling demonstrates the signalling system's ability to meet Journey Time Capability and Capacity specifications under the PPP. One simulation I saw covered Edgware Road handling 30 trains an hour, including turned backs.