Signal failures on the Northern Line cost travellers more than 100,000 hours in delays in just two months, new Transport for London figures show.
The number, based on the five longest delays in September and October, is the extra journey time calculated for all passengers combined.
The Northern Line recorded the highest number of lost customer hours as a result of signal failures across the whole network during that period.
In total, signal failures accounted for the three biggest delays on the line, racking up a whopping 98,000 lost customer hours.
Defective trains and customer issues – for example trespassing, setting off alarms, altercations – accounted for the fourth and fifth worst delays, amounting to almost 16,000 lost hours combined.
TfL is in the process of replacing the Northern Line’s dated signals, which are more than 50 years old, with an automated system, as well as replacing track on several sections.
The transport provider, which hopes to complete the work later this year, says capacity will increase by 20 per cent – an extra 11,000 passengers per hour – and claims journey times will be reduced by 18 per cent.
A TfL spokesman said: “The Northern Line has the most branches of any other tube line and it is complicated to keep it going – but it is our job to keep it going and the improvements to the signalling system will help.”