Minutes saved on the West Coast Main Line represents millions of pounds in increased rail traffic.
Which is why work to speed up the junction at Ledburn near Leighton Buzzard is under way.
Diarmaid Fleming reports.
Ledburn Junction on the West Coast Main Line is best known as the scene of the Great Train Robbery in 1963. Today, a project involving even more intricate planning - and worth close to the £2.3M stolen then if things go wrong - is under way.
Alongside the infamous bridge where Ronnie Biggs, Buster Edwards and their villainous colleagues plundered the London-Glasgow mail train, a series of cross-over points form a 'ladder junction', enabling trains to move between any of the four tracks, two fast and two slow. Ladder junctions, generally around 16km apart, enable fast passenger trains on mixed traffic routes to pass slower freight or local trains travelling in the same direction.
The track configuration and technology currently in use at Ledburn Junction is not very different to that used 40 years ago, forcing trains to slow to around 30km/h when negotiating the stretch. The present work to upgrade the junction uses the most modern switch and crossing rail kit available in the UK, and will enable trains to pass at close to 100km/h.
'It's not like slowing a car down to 30km/h from 100km/h: a train must decelerate and slow down for a significant distance before reaching the junction, and then accelerate to build up speed again. At a slow junction like this there is a considerable cost in minutes. Improving the junction and increasing speeds saves time and allows considerably more train paths, ' explains Balfour Beatty Rail Projects project manager Adam Stuart.
For the passenger it means more and faster trains. And for Network Rail and the train operators, that means more revenue.
Not surprisingly, work on the UK's busiest stretch of track, part of the primary rail artery to Scotland and the North, has required minute planning. Maximum efficiency has been needed to ensure best use is made of time when the lines are closed to trains. While work continues during the week, the bulk is done during block possessions at the weekend. 'As with many rail jobs here, the logistics create a greater challenge than the engineering. For weekend work during possessions, planning is almost on a minute by minute basis, ' says Stuart, pointing to programming bar charts scaled in units of 15 minutes.
The contract was signed before the dissolution of Railtrack. It involves track work, overhead line work, signalling and commissioning, all expected to be complete by Easter 2003.
Overhead line work and gantry erection for the new track layout began in December 2001 and is well under way. New gantries are 50m-60m apart, determining the length of new track sections which can be installed.
An entirely new junction is being built on the 'up', or London, side of the old ladder crossing. Put at its simplest, Balfour Beatty's track work involves ripping out the old crossovers and replacing them with straight track. Eight new crossovers are being installed along a 1km stretch of what was previously old straight track.
Before laying new tracks, the stone ballast was tamped to ensure the rails were correctly levelled, while the horizontal alignment was checked to see the track conformed with the design arrangement. As a result correctly configured track provides an accurate template into which the new trackwork will fit.
Switches, with long 'bearers' running the width of the points, are made up and assembled off site in Nottinghamshire by Balfour Beatty Track Systems.
Once assembled and checked for dimensions and fit, the switches and crossings are dismantled and brought to site by truck where they are reassembled and once again checked for dimensional accuracy. This is part of the exhaustive planning process needed to ensure maximum efficiency during the possessions.
'Until relatively recently all switches and crossings were on timber sleepers, ' says Stuart. 'If holes on a long bearer plate did not fit, then there was always the option to drill on site. But with concrete sleepers you don't have that luxury: everything has to be bang-on, with only a 2mm margin for error.' Trains rumbling past the site office are a constant reminder of the savage penalties if anything going wrong, holding up services and forcing compensation of train companies.
'When you consider the cost of an overrun on a Monday morning if the track didn't fit, the cost of assembly and reassembly to check beforehand is not much, ' says Stuart. 'We've never had an overrun. While fewer trains will be affected immediately after a possession that ends at 5am than in the rush-hour, if you had a longer overrun the cost could still run into hundreds of thousands of pounds - probably half a million pounds by lunchtime, ' Stuart says solemnly.
Possessions can include a complete shutdown of all four lines from 3am on Saturday until 5am on Monday, with two lines shut additionally from 9.30pm on Friday. Other possessions have limited a full weekend block to two lines, with the other two only partially shut to allow some traffic through the essential artery to the north.
Engineering works trains, some up to 400m long, arrive for each possession, carrying ballast and plain or straight sections of track, as well as wagons to shift materials and machinery around.
Once the old track is removed, ballast is excavated to ground formation level, and the stretch reballasted to around 50mm below sleeper level. The operation to move new track into place is highly mechanised - the days of large railway gangs a thing of the past. A giant Kirow crane capable of lifting 30t at a 15m radius with the jib horizontal - one of only two in the country - is invaluable in lifting materials and plant into position within the narrow confines of overhead lines and gantries.
Track sections are inched into position using the Geismar PLUMS machine, which looks like a giant mechanical centipede with legs and wheels. This ingenious piece of plant can lift a track section, 'walk' it onto the correct track location, and then roll it into position for final fixing. Hydraulic jacks lift the sections, with the machine's 'legs' moving it sideways to its location.
The track then rests on the PLUMS' bogies, where a works train loco pulls or pushes it into position. One operator controls each PLUM unit, with 19 of the machines used to shift the biggest switch section. Safety is a paramount concern. Stuart says that since the installation of the permanent way began, 85,000 man-hours have been worked without one reportable three-day injury.
Although the new crossings are locked into position to enable straight running of trains, the Potters Bar accident last May has meant rigid enforcement of rules regarding signalling at switches and crossings by the Railway Inspectorate, with all electrical and signalling work to be completed within six months of installation of the track. This work, being carried out by Westinghouse, is due for completion around the turn of the year, for commissioning by April.
Civils work associated with the project includes construction of substantial earth berms on one side of the railway embankment - tamping records indicated excessive settlement on one side of the tracks.
Cementation Skanska is carrying out these works to provide additional stability.
A robust approach to service installation has also been adopted - rather than run services under the tracks through trenches, service ducts running 5m below the track are being installed by directional drilling rigs. These ducts will run between shafts constructed either side of the line, formed with precast reinforced concrete ring segments.
'The old way involved digging trenches under the track and backfilling. If there is insufficient compaction, the ballast can settle, allowing a twist fault to develop in the track, which means expensive maintenance work. This new way of services installation using the shafts may cost more initially, but provides a better and cheaper solution in the long run, ' says Stuart.