When it comes to rolling stock on the Underground, it has become very easy in recent years to focus on the new. We have seen new trains on both the Victoria and the Sub-surface lines and we have seen the official launch of the “New Train for London” (NTfL) programme – TfL’s plan to replace all “deep tube” stock with a single, universal new train. What is easy to forget, however, is that NTfL will not be seen until the first half of the 2020s at the earliest and, as the supporting documents for the latest TfL Board Meeting help demonstrate, this presents some interesting maintenance challenges in the short term – not least for the Bakerloo Line.

The situation so far

We wrote extensively about the current NTfL proposal at the end of last year. Despite its billing (primarily by press and politicians rather than TfL themselves) as a “driverless” train for the future it will more than likely feature a driver (or at least be manned) for a significant portion of its time in service. Whilst debate after the announcement focused on this, and issues such as air-conditioning and funding what went largely un-noticed outside of the rail industry itself was the planned rollout date.

The NTfL concept

As we wrote at the time:

TfL have confirmed that the current schedule for deployment begins with the Piccadilly Line in 2022, to be finished by 2025. This is to be followed by the Bakerloo Line, completing in 2027 and the Central Line/Waterloo & City to be completed by 2032.

This is not an unnatural timescale for a project of this size – indeed those timescales themselves have likely been revised upwards slightly since, as more research and funding issues affect the project. For the average commuter, however, it is a long time indeed. In the context of the lifespan of the Bakerloo Line’s existing trains, it is arguably even longer still. The 72 Stock already found on the line has already been in service for over 42 years. By the time of withdrawal, it will be over 55 years old.

Rebuild and refurb

Life extension works and the refurbishment of old trains is, of course, nothing new. Indeed it has been a regular activity on the Underground for a number of years. There is even life for old Underground trains beyond the boundaries of the Capital – both in their traditional home on the Isle of Wight and in more modern, creative ways thanks to companies like Vivarail, who plan to refurbish old D-Stock into “D-Trains” in order to service the UK’s high demand for diesel rolling stock.

As a London Underground report included in the latest board papers shows, however, extending the life of the 72 Stock is not going to be as simple a task as hoped.

A lack of surprises

Some kind of life-extension work on the 72 Stock has always been planned. Even ignoring the fact that its nominal life-span was 40 years, a London Underground condition study back in June 2013 had concluded that repairs were needed within four years to ensure the fleet continued to meet relevant safety standards regarding performance in a collision or derailment. With the announcement that the Bakerloo would not receive the NTfL until 2025 at the earliest a full programme of renewal effectively became guaranteed and work began to assess just how extensive the work would need to be.

Estimates as to the work required were made, and a rough costing of £30m for the work established. As with many elements of maintenance and renewal however, the only way to truly establish the likely scope of what would be required was to take one (or more) 72s apart and see.

London Underground thus approached the board and sought permission to begin the process of putting three complete trains through the repair process, the goal being both to develop a production line methodology to use going forward on the remaining 33 trains and, more importantly, to truly establish what state the 72s are in and the level of repairs required.

Worse than planned

Unfortunately the results of this investigative work are far from pretty:

During repairs to the first train it has become apparent that the overall condition of the bodywork and under frame is in a worse condition than originally concluded. It is considered that the findings from this first train are representative of the condition of the remaining fleet.

It should be thoroughly emphasised that none of the damage discovered poses a short-term threat to the safety of the trains, but it does mean significant repair work will be necessary in order to keep the 72s in service until the NTfL arrives. Levels of corrosion, for example, have proven to be far higher than expected. Car body corner posts were initially planned to be replaced only as required, but all four on train 1 were found to be corroded beyond repair. Similarly it was expected that the saloon floors would only require partial replacement. Again, instead, train 1 showed extensive corrosion necessitating full replacement. Unexpected sole bar damage and corrosion were also discovered, and both external and inner door pillars were found to be cracked beyond repair. The side panel stiffeners were also in a far worse condition than expected.

Swan neck cracks (left) and after repair (right).

Corner post corrosion before and after repair

The scale of the work now required also means it will likely be difficult to repair the trains in the existing facilities at Stonebridge Park depot, and thus new workshop space will also likely be required. To this end, London Underground have suggested the creation of a dedicated workshop facility at Acton Works to allow London Underground’s own Train’s Division to carry out the work, with a new road-ramp constructed at Stonebridge Park to allow trains to be split apart and carried to the works by road when rail paths are unavailable.

Clockwise from left: corroded internal door pillar, floor plate corrosion, corroded kick plate, cracked external door

None of this will be cheap. According to London Underground’s revised estimates, this now means that the full cost of the replacement programme will be closer to £70m, twice the original estimate.

Given the pessimistic picture of the state of the 72 stock that the report paints, this seems a reasonable price for the work. One that TfL would likely much rather not pay, perhaps, but which it has little choice but to shoulder. Taking a different approach would simply defer and increase the cost of maintenance (and chance of disruption) down the line.

The simple fact is that unfortunately the age of the 72 stock means that in engineering terms it is well and truly on the far end of the bathtub curve. And as the report itself bluntly concludes, with its replacement over ten years away:

There is no “do nothing” option.

Cover photo, showing a unit of 72 Stock at Kilburn High Road, by Oxyman