Delays and overcrowding caused by the part-closure of the Piccadilly line should start to ease by the “end of January”, Transport for London has promised.
Problems with worn-out wheels have caused a dire shortage of trains on the line, with only 60 of the 86 trains in the Piccadilly line fleet able to be used on Tuesday.
But TfL chiefs hope to have 70 trains repaired and back in service in the next two to three weeks, meaning the western end of the line between Rayners Lane and Uxbridge can be reopened.
This will have a hugely beneficial impact on the rest of the line as it will mean more trains per hour, especially at peak times, which will reduce overcrowding.
Passengers have suffered delays of up to 17 minutes between Piccadilly line trains (Ross Lydall)
Bogie men: the Piccadilly line depot at Oakwood (Ross Lydall)
At present, passengers in the Hounslow area have reported gaps of up to 17 minutes between trains.
A total of 75 Piccadilly line trains are required to operate a normal peak hours timetable.
The line is one of the busiest on the London Underground, linking the West End and Heathrow airport and being used for one in 10 Tube journeys.
The problems began in mid-November when two storms caused a deluge of leaves to fall on the line’s outer London “overground” sections.
These leaves formed a “very slippery” leaf mulch on the rails that caused the 50-year-old trains to lose traction and skid – creating “wheel flats”, or flat, worn, ground-down areas – on virtually every Piccadilly line train.
The wheel flats can develop into “cavities”, causing “banging” between the train and the rails.
Bumpy ride: One of the ‘wheel flats’ on a Piccadilly line train wheel (TfL)
When the defect exceeds a size of 50mm, this requires the trains to be taken out of service to have the wheels reshaped using a giant “lathe” or cutting tool, which returns the wheels to a circular shape.
Marc Perry, the Piccadilly line’s fleet manager, said the six-carriage trains had to be split into two three-carriage sections to enable them to be worked on in Tube depots.
The Tube carriages are lifted off their “bogies” or wheel sets – there are 24 axles, each containing four wheels on each train – to allow the 96 wheels to be repaired.
The wheels are taken by lorry from Oakwood depot to be re-shaped at the Piccadilly line’s other depot, in Northfields.
Alternatively, trains can be driven straight on to the lathe at Northfields, avoiding the need to take them apart.
Bumpy ride: the wheel flats cause the Piccadilly line trains to run unevenly on the track (Ross Lydall)
Extra wheel repair work is also being done at the Victoria line’s Northumberland Park depot and the District line depot in Upminster to speed up the process.
It can take three days to fully repair a train if all 96 wheels are damaged.
Richard Jones, TfL’s director of asset performance delivery, said repair teams had started to get on top of the problem since Christmas as fewer trains were suffering wheel damage.
“The rate of new flats has dramatically reduced,” he said. “The frequency in the core [central London] section is improving as we put more and more trains back on the railway.
“Once we have got to a certain number [of trains], we will be in a position to put that part of the line between Ruislip and Uxbridge back into service. If we can bring that date forward, we will do.”
The first of 94 new trains on the Piccadilly line is due to enter passenger service at the end of 2025 (Siemens Mobility)
Unlike newer Tube trains, including the new fleet of Piccadilly line trains that is due to start entering service at the end of 2025, the Piccadilly line’s 1973 stock of trains does not have “wheel slide protection”, a form of ABS anti-lock brakes seen in cars.
Mr Jones said: “At the moment, we are recovering from a very challenging leaf fall, where a significant number of trains have been damaged.
“The wheels on the trains have been effectively ‘flatted’ as a result of slip-slide incidents because of leaf fall.
“The repair itself is not difficult but it is quite time-consuming, in terms of getting to the wheels. Disassembling the train is the bit that takes the time.”
Asked why leaves could cause such problems, Mr Jones said: “Quite a significant proportion of the Piccadilly line is above ground.
“Everyone thinks about the Underground [section], but the ends of the line are above ground. They run through some quite leafy parts of London.
“This is a problem, not just on the Piccadilly line but a number of lines.
“The way that the [autumn] season has played out, particularly with two very severe storms we experienced, those two weekends caused an awful lot of damage over a very short period, which we are taking quite a bit of time to recover from.”
TfL said problems with train motors had also been responsible for a shortage of rolling stock on the line. Services west of Acton Town have been particularly badly affected.
In an email update to passengers, TfL said: “While we continue to make good progress in repairing the damaged train wheels, our fleet shortages have been impacted by a number of damaged train motors caused by recent poor weather.
“We are working as quickly as possible to repair the damaged motors to enable a full service to be restored by late January.”