District line image taken at Temple station
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Analysis: District line Tube delays likely to continue under outdated signalling system

Image credit: Ben Heubl

An E&T analysis of data regarding delays on London's Tube network and interviews with underground staff suggest customer frustration is likely to persist as long as old-fashioned signalling systems from the 1980s are not upgraded. Nonetheless, the long-term trend for the District line suggests that lost customer hours are on the wane and not on the rise.

Ask Londoners who make frequent use of the city's underground rail network, and many will tell you that the worst Tube line in terms of signal failure delays is the District line service. While the green used to show the line's route on maps is a colour often associated with hope, many customers have all but given up on it in favour of alternative routes. 

The latest performance statistics published by Transport for London (TfL) suggest that lost hours caused by signal failures have reached unprecedented heights.

Many passengers must feel that record levels of problems confirm their perception that delays are increasing. And with a lot of failures occurring during the morning rush hour, between 06:30 and 09:30, the experience of customers going to work between those hours may be aggravated and their mood dampened.

But are signal failures and lost consumer hours on the District line really on the rise? To find out, E&T took an in-depth look at a wealth of data which is made available by TfL for as far back as 2003/2004.

In recent months, unusually high average monthly rates in lost customer hours were recorded by TfL for the District line. Within the first two four-week periods for the 2019/2020 season, these latest figures stand out and prompt questions.

With 101,011 lost customer hours in April (62 per cent higher in 2019/20 than the monthly average between 2003/04 and 2018/19) and 104,480 (109 per cent higher) for the May four-week period, increased dissatisfaction and impatience for anyone reading those figures may perhaps be understandable.

At a grander scale, the figure for lost customer hours relative to each period is not exclusively limited to the District line, nor restricted to signal failures, as the data shows.

Lost customer hours across all tube lines

Image credit: E&T, Ben Heubl

E&T inquiries show that these figures and graphics should not be taken at face value. The truth is more complex. The first two periods of 2019/2020 appear to be outliers, for two reasons, according to the TFL press office. On one hand, the analytics team started to change how 'lost customer hours' for the season 2019/20 is being calculated. According to Sean Colfer, senior press officer at TFL, the new formula will better reflect the network in 2019. "The formula we were working with previously hadn’t changed in about a decade, when the Tube has changed quite a lot in that time with new signalling, station upgrades and other stuff having finished". As a result, values this year aren’t really totally comparable to previous years,  he said. This would have altered and boosted the latest figures as a result. 

The second reason is more unavoidable. The District line's signalling system is old and requires updating urgently. In an interview with TfL Help team member on the District line, E&T was told that upgrades are expected but not any time soon. "We [the District line] are still using [a signalling system] from the eighties. [The old system in place] is part of the reason why the District line has so many signal failures on our line because we are using an antiquated system," the member of staff said. 

An improvement programme - the Four Lines Modernisation programme - is in progress and is said to have the ability to increase capacity on the District, Circle, Hammersmith & City and Metropolitan lines by 33 per cent, according to an official statement. But customers need to be patient. The first section of new digital signalling went live in March 2019 between Hammersmith and Latimer Road, but the whole programme is not due to be completed before 2023. 

Failures happen infrequently, the District line station staff member said: "It can happen at any point. But what I have noticed is that if one happens, normally it happens a few days in a row. There are so many factors that go into why signal failures occur. Most commonly, it will be a computer failure, servers have gone down. Those ones are the quick ones that get resolved in 20 minutes". 

"The Central line, the Piccadilly line, the Victoria line, have all got a much better system", he explained. There, the trains move pretty much in unison, "whereas the District and Circle, they are really old lines", he said. 

To the question of whether signal-related delays occur more frequently on the District line, the answer considering the whole data since 2003/04 is no. E&T can show that the long-term trend is promising and there is clearly an ongoing decline in lost customer hours. Average lost customer hours caused by signal failures in the year of 2016/17 were found to be at almost half the rate as for 2004/05. This is an achievement given that the signalling infrastructure is not getting any younger.

More visual proof provides a graphic showing a regression analysis across the 13 four week periods - ranging from April to the end of March in the following year*.

In the event of a delay on the District line, the best advice by the member of staff at Temple is to complain to customer services. A quick response is given via Twitter. The District line also has its own Twitter feed, with nearly 114,000 followers. 

*There are 13 periods and not 12 because periods are set at exactly 4 weeks each, totalling 13 annual periods

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