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Signal change

The Jubilee Line Extension has begun operations with conventional versions of signalling and other high technology integrated control systems. Adrian Greeman explains why.

There were already signs in 1997 that all was not well with development on the Jubilee Line Extension's planned high-tech moving block train control and signalling system.

Jubilee Line had been chosen by London Underground to pioneer a new generation of computer controlled signalling systems which, when commissioned, could revolutionise the Tube network, boosting capacity by up to 50%.

In response to growing doubts about development progress being made by contractor Westinghouse, and in the knowledge that any delay could seriously impact the line's opening date, a shadow team was set up by the JLE project to look at contingencies.

'We started working in parallel to consider a conventional fixed block alternative,' says David Waboso, commissioning manager at the JLE who since 1996 has been seconded to the project from management consultant Nichols Group. 'Initially this was really just as a back-up. It was quite a while before the realisation dawned that we really were not going to make it with the main system.'

Westinghouse had been signed up to develop a new computerised system for the line. By continuous radio interchange of data between the trains, lineside computers and a central control, trains would run much closer together but remain safe. Just how close would depend on train speed and location, with the system calculating a continuous stopping 'envelope' which moved along with the train. Unlike the fixed blocks in conventional signal systems, the moving envelope gets smaller as speed decreases.

The computer, tracking every train on a geographic map would make sure no other train entered its envelope, sending cab displayed warnings to following trains and triggering automatic braking overrides if necessary.

The Westinghouse system was to give an hourly line capacity of 36 trains, 50% more than the 24 trains per hour (tph) with which the Jubilee Line will now achieve with a conventional system.

However it was not until February 1998 that Westinghouse finally conceded that development was tougher than it had originally thought and acknowledged that it would have to break the deadlines. Unfortunately, by then JLE was committed to this complex technology, as the then project director Hugh Doherty told NCE last year (NCE 21 May 1998).

Signals now run on a re-engineered version of the intended system, with the equipment modified to work as conventional fixed block. 'It is rather like having a four-wheel drive Jaguar but only being able to use it in two-wheel drive mode,' says Waboso.

The main changes were to the software, which dominates signalling. Despite initial reluctance by Westinghouse, Waboso says the firm pitched in well to make the modifications 'perhaps because at the technical level the guys all speak the same language'.

Waboso explains: 'The transition was relatively smooth and the big thing for me is that the team proved equal to it.'

Hardware changes were also made, with a consequent impact on dozens of other contracts. Moving block does not use visual signals, other than a skeleton set of red/green indicators for emergencies. To transfer to a fixed block required changes.

'There is more lineside infrastructure needed, cabling, signal lights and so on,' explains Waboso. That in turn meant altering the tunnel in places and other physical changes. 'There was a fair amount ofre-engineering,' he says.

There was also a cascade of effects at the many interfaces with services, traction power supply, platform edge doors and so forth. 'The project team found itself in the centre having to talk to all these contractors and modify their contracts,' recalls Waboso.

As a result of this experience JLE has looked again at its other hi- tech systems and carried out similar 'de-risking', says Waboso. The whole line was conceived as a high-tech communications project with a series of integrated control systems for everything from public address and variable signage information displays, to fire control systems, lighting and security.

A west London control centre works with a universal workstation. Central Information Management systems - CIMS, and a Supervisory Control & Data Acquisition - SCADA system pull together incoming data and outgoing instructions for every possible function. These include signalling, traction power, tunnel ventilation, public address and fire alarm systems. Each station has a local version of this which interconnects with the west London control centre.

'Some of these systems have been topped with their own stand-alone head,' says Waboso. For example, tunnel ventilation will not yet be fed in through the other systems, he says, as significant amounts of time were saved in commissioning.

Eventually it is hoped that the software and systems will be developed and integrated, to operate as intended via a single control screen. In the future it is also hoped that the signalling too will be upgraded to handle the higher train service frequencies required by the increasing passenger demand. Westinghouse is still contracted to deliver, he says.

But with the millennium deadline looming, emphasis has moved away from developing the new technology towards getting the trains running and stations working. If LUL is to expand its passenger carrying capacity from the introduction of an advanced train control system the question still remains, how and when?

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