Signal failure is the biggest single factor that caused delays on the District Line in 2014/15, which will come as little surprise to its passengers. 35% of the time lost though delays was caused by signal problems compared to just 14% for the whole Tube network
Transport for London measures delays in what it calls Lost Customer Hours (LCH). These are calculated by multiplying the delays in minutes by the number of passengers. TfL records all delays over 2 minutes. It uses the financial year from April to March and splits the year in 13 equal periods for performance measurement.
Data in the London Underground Performance Almanac for the last full year shows there was an average of 222,088 Lost Customer Hours per period on the line. This makes it the third highest on the network.
Over the past 10 years as Lost Customer Hours have been reduced across the network the District line has reduced LCH by 57% comparing the average for 2003/06 with 2012/15.
TfL’s next round of modernisation work will target 3 of the oldest tube lines, including the District line, to upgrade a signaling system that the company says “belongs in a museum, having been operating safely, but in a very basic way, since the early years of the last century.”