Four of London Underground’s lines suffer from a bit of an identity crisis. Individually they are well known; the Circle, District, Metropolitan and Hammersmith & City lines are familiar to both Londoners and visitors – they are the yellow, green, maroon and pink lines on the Underground map.

However, they are not truly discrete railways. They run on the same lines and now even share the same trains, although some are longer than others due to variations in platform length and the seating arrangements are different on the longer-distance Metropolitan trains.

So really they need to be considered as parts of a larger whole. But what to call it?

“The Underground” is an option, but that includes all of the lines on the LU network.

Foreigners who like to give the impression they are at home in London talk about “The Tube”, again really meaning the entire network. The Tube, or the Deep Tube, more properly refers to the small-diameter tunnels (and trains) of the Bakerloo, Central, Piccadilly, Northern, Waterloo & City, Victoria and Jubilee lines. Built at different times by different companies, their tunnel diameters vary and there is almost no interconnection between them.

Largely built by cut-and-cover techniques, and running at ground level in many places, the four lines that form the subject of this article have been called the Sub-Surface Lines (SSL) and they make up the Sub-Surface Railway (SSR). So when it became time to completely replace the signalling systems with a single, modern, digital system, the project became the Sub-Surface Lines Resignalling Programme.

Add in some more work to the infrastructure, and it became the Sub-Surface Upgrade Programme.

But, as programme director Stuart Harvey readily admits, that was hard to explain to the public. All underground lines are sub-surface, aren’t they? So which ones were being worked on?

To make it simpler, along came another acronym – 4LM. The Four Lines Modernisation programme brings together new rolling stock, new signalling, improved power supplies, upgraded track, better station access and a host of other improvements into one scheme that is easier for passengers to understand.

Most of the trains have now been replaced by Bombardier S Stock trains, designed and manufactured in Derby – there are just a few of the D78 trains left on the District line and they will be gone later this year.

That leaves the signalling. When the S Stock was first designed, space was left in the cab for the installation of equipment to be manufactured by Westinghouse. That initiative foundered, and Bombardier took the signalling on itself. More recently, after successfully installing a CBTC (communications-based train control) system on the Jubilee and Northern lines, Thales was awarded the contract for renewing the signalling on the whole SSR – all four SSL – as part of 4LM.

That was just a year ago. Since then, a lot of progress has been made so it is high time for a review, and hopefully a simple explanation.

First V1, now V2

Due to its previous experience with the successful implementation of its SelTrac on the Jubilee and Northern lines, Thales was able to hit the ground running. A modified version of the existing software was quickly developed and a brand-new S Stock train fitted out with a temporary installation of aerials, sensors and a rack of control equipment on a trestle table in the passenger compartment.

This is test train V1. Running at Old Dalby (otherwise known as RIDC Melton), it has been testing the ATO (automatic train operation) by stopping and starting at mock ‘stations’ and opening and closing its doors. Rail Engineer went for a ride a few months ago (issue 138, April 2016) and, despite the temporary appearance of the modifications and the amount of sticky tape involved, it all worked flawlessly.

The control gear, a host of similar grey cabinets, was housed in a couple of temporary buildings.

Matt Buck - Farringdon_station_MMB_22_S-Stock

Photo: Matt Buck.

Since that visit to the test track, the train is now running at the test track’s line speed of 80km/h, proving the system design. An upgrade to the software, making it more akin to that needed to run the highly complex four-line network, has also just started being evaluated.

Test train V2 is almost ready. This is a second S Stock train which is being fitted out at Bombardier with all of the equipment where it is meant to be – racks of electronics in a cabinet in the driver’s cab, wiring hidden from sight in the on-board conduits, aerials and sensors discretely located in their final positions. In all, around 2,000 wiring changes were needed during the fit out.

Once complete, which should be by the time this article goes to press, V2 will be off to Old Dalby to continue the test programme.

Aim for P0, not P90

Most railway projects have a target completion date. This usually contains some contingency, but if that proves to be insufficient then the project either overruns or has to be curtailed.

4LM is being managed under a completely different premise. Two completion dates were calculated. P0 assumed no risk and everything going to plan, while P90 imagined 90 per cent risk. The difference in the two dates is 18 months over the life of the project.

“We all know that P0 is impossible to achieve,” Stuart Harvey explained. “But nevertheless we are going for it and managing the risks as we go along. We feel it is a far better way of doing things than having an artificial end date with ill-defined contingencies. We did it this way on the Northern line, and we ended up eight months early!

“Currently, after one year, we are only 11 weeks over a P0 schedule, and under cost as well.”

One year on

Andy Bell, the Thales project director, reflected on the first year of the 4LM programme.

“It’s been a busy year,” he told Rail Engineer. “Getting a project the size of 4LM up and running is a big undertaking. We have a collective organisation of 1,000 people working on design, on software, on site and at Old Dalby.

“We have also engaged with key subcontractors, such as Bombardier for the work on the V1 and V2 trains, Kelly ITS to help with installation, VolkerRail on track and DEG Signal on design.

“One of the key things we looked at was collaboration and how the team works together. Getting relationships in place was crucial to setting up the project the right way.”

Stuart Harvey agreed. “LU and Thales have a very intrusive arrangement,” he stated. “I have to deliver to Andy as much as he delivers to me. We will fail if we don’t collaborate.”

Starting with the software used successfully on the Northern line, 150 new functions will need to be built into the program for 4LM. The first tests at Old Dalby incorporated 20 per cent of those while the latest update includes another 20 per cent.

To commence running on the network, the first 60 per cent will have to be in place, an upgrade which is due in January 2017. On-track testing will commence between Hammersmith and Paddington in June next year.

The remaining additional functions will be needed once trains start running over shared lines and interfacing with Network Rail infrastructure at Wimbledon and Harrow. Still more will allow the system to be fitted to engineering trains.

Infrastructure work

Out on the network, the new SelTrac system will need three specific modifications to the current infrastructure.

A ‘tag’, basically a powered-but-passive RFID (radio-frequency identification) tag, will be fixed to the trackbed between the rails every 25 metres or so along the 314km of the railway. A tag reader, mounted under the train, will identify the tag and use that information to get an accurate positional ‘fix’ for the train.

Between tags, and if a tag is missing or broken, the train’s onboard software will use information from axle-mounted tachometers to calculate the distance since the last tag – and then correct that information when the next tag is read.

There will also be axle counters, Thales’ own, to be used to detect trains that aren’t equipped with SelTrac (mainline trains on Network Rail infrastructure, non-LU engineering trains) and in times of perturbation when working in degraded mode.

Accurate stopping, particularly important if platform screen doors are ever to be installed later, will be managed through a combination of tags and axle counters. The driver, however, will have full visibility of the process.

The train communicates with the control centre by radio. As radio waves don’t travel well along tunnels, even with reflections off the walls and roof, transmission has to be more-or-less by line of sight. Radio repeaters will therefore be mounted in the tunnels every 200 metres on average, closer in areas of tight curves.

This is one of the main differences from the Jubilee and Northern line installations, which use radiating cables to communicate with the trains. “Radio is much better,” stated Stuart Harvey. “We have had incidents with power collection shoes coming off trains and cutting the cable, so radio should be much more reliable.”

Four Lines Modernisation map

While a lot of the equipment can be installed overnight, there will be three weekend closures on the Hammersmith to Paddington section to ensure that the new system will interface with the existing interlockings.


It is clear that Thales is drawing, not only from its own work in the UK, but also from its international projects. “We are a global business,” explained Andy Bell. However, the 4LM project is probably the largest metro installation of a CBTC system in the world, particularly on a ‘brownfield site’, so a lot of the experience has to be taken from the company’s success on the Jubilee and Northern lines.

“Under the old signalling system,” Stuart Harvey commented, “when we had a failure on the Jubilee line, it took all day to recover from it. When Thales came in, we had the service back in 20 to 30 minutes. That was the biggest change.”

This should be even more apparent on the four sub-surface lines, as the system is ‘colour blind’. If the new control centre at Hammersmith needs to recover the system, it will not give priority to any one line (colour), it will choose the best and quickest way to recover the whole network.

However, this wasn’t the first thing that sprang to mind when London Underground was asked what stands out about this project.

“The most impressive thing is the way that London Underground, Thales and Bombardier have worked together,” Stuart Harvey commented.

His boss agreed. Talking to Rail Engineer about the project, LU managing director Mark Wild stated: “I am impressed by the way everyone has worked together. London Underground, Thales and Bombardier have worked as one team and are making good progress on this challenging project.”

So that is the state of play on 4LM, one year in. In a year’s time, by July 2017, trials will have already started on the first section of the network and trains will start being fitted with the hardware they will need. If the current rate of progress continues, then the Circle line could be running under SelTrac CBTC as early as 2019, only four years after the project started – and that will truly be impressive.