16.07.08
Brake testing on the Jubilee Line
The Jubilee Line is a vital transport artery through London carrying over 600,000 people daily. This is a significant increase on passenger numbers a few years ago as demand is rising faster than ever anticipated. Drivers for growth include the ongoing construction of skyscrapers in Canary Wharf and entertainment venues, the enlarged Wembley Stadium and the huge O2 arena in Greenwich
Capacity on the line was increased by 17% at the end of 2004 when Tube Lines added an extra carriage to every train. That much-needed space was quickly swallowed up and further capacity improvements are keenly required. Tube Lines is making steady progress towards a full line upgrade – the first on the Underground under the public private partnership – which will see trains safely running faster and more frequently.
Scheduled to go live in late 2009, the key to increasing capacity by a further 23% is a state of the art signalling system. The “transmission based train control” system chosen by Tube Lines is a more advanced version of the one used on the Docklands Light Railway, and the same as the one on the much-admired Hong Kong metro (MTR). With a strong record and solid credentials from around the world, the Jubilee Line can look forward to excellent levels of reliability.
What is different about the application of the advanced train control system on the Jubilee Line, however, and where the real challenge for Tube Lines lies, is in installing it on an operational railway. Those 600,000-plus passengers still have to get to work each day so the installation and rigorous testing has to take place during the four hours or so each night that trains don’t run, fitting in alongside regular maintenance, or during occasional weekend closures.
One of the latest series of tests looked at brake performance of Jubilee Line trains. One way the upgraded system increases capacity is by automatically controlling trains at the highest possible speeds. It will accelerate trains faster and make them brake more sharply. The higher average speeds require a sophisticated level of understanding about how the brakes operate so Tube Lines investigated. Preliminary testing looked at an empty train but on a recent Saturday night when the Jubilee Line was closed to passengers, emergency brake testing took place on a train weighed down to simulate rush hour.
To ensure consistent test results, the same train was used for both sets of measurements. It was specifically selected according to its brake wear rate to guarantee findings were representative of the fleet as a whole.
Hundreds of weights were carefully spread throughout this regular Jubilee Line train. At peak times, passengers and their luggage can weigh over 90 tonnes so Tube Lines used this many weights to simulate a fully loaded train. Clearly the weight on board has a significant impact on brake performance.
Throughout the night, the train was driven along the Jubilee Line and its emergency brakes applied at specific intervals, including at the steepest slopes near Bermondsey and west of Canning Town, where the track dives underground and passes under the Thames. Measurements of stopping distances are being compared with the preliminary findings from the empty train and with standard industry figures for train braking.
As well as stopping distances, further measurements were taken. For example, temperature sensors embedded in the brake blocks took readings which are being used with sophisticated computer modelling programmes to aid system designs.
Safety is non-negotiable so every eventuality must be planned for. In one series of tests, some brakes were disabled to simulate the worst possible conditions a passenger train might encounter. These findings will also go towards finessing the details of the new system to ensure trains stop safely every time.
Organising the logistics of the testing was a significant challenge for the project team, involving careful co-ordination between many groups. Trans Plant, Tube Lines’ division providing specialist engineering trains, delivered the required weights to the Jubilee Line depot in Stratford. There, a team of four people from Metronet completed the heavy work of loading the 720 weights onto and off the test train. London Underground signallers directed the trains involved.
The Tube Lines project team liaised closely with its operational counterparts and fleet maintainers from Alstom throughout the weekend when tests were conducted and ensured the train used in the tests was ready for passenger service on Monday morning. Emergency braking poses the risk of “flats” on wheels, which result in uncomfortable journeys for passengers and extra wear on rails. Tube Lines’ wheel lathe was therefore put on standby ready to grind the wheels back into perfect circles, although in the event it was not necessary.
David Orme, Tube Lines’ project engineer who led the tests, summed up the testing. “It gives a whole new meaning to the concept of ‘weighting’ for a train,” he said. “The tests we completed will help us identify the intricate details of the new signalling system. When it’s introduced next year, passengers’ journeys along the Jubilee Lline will be faster and people will have to wait less time for a train.”
With Tube Lines seeking to realise its vision of delivering an outstanding Tube for London, increased capacity through faster journeys and shorter waiting times for passengers, coupled with improved reliability, are exactly what is needed.
Tell us what you think – have your say below, or email us directly at [email protected]