The upgrade will mean we can carry an extra 11,000 passengers per hour which is equivalent to a fifth more passengers. Journey times will also be reduced by 18 per cent.
Major progress has been made with the Northern line upgrade, with new state-of-the-art signalling now live on the first section of the line between West Finchley and High Barnet.
Transport for London (TfL) has taken a new approach to delivering the upgrade to the Northern line with far fewer closures than the PPP-era Jubilee line upgrade, and a reduction in disrupted journeys of 60 per cent.
TfL is also doing more testing "off site" to resolve problems before the new signalling is introduced to the railway, meaning greater reliability for customers.
London Underground (LU) has also intensified the amount of work done during night-time engineering hours, utilising every minute the network is closed to carry out upgrade works, as well as the usual maintenance work.
So instead of the 18 months of weekday closures that were originally planned for the whole line under PPP arrangements, LU implemented slightly later Sunday morning start-ups on the High Barnet and Edgware branches, when less people are travelling.
This has allowed LU to extend night-time works on Saturdays without requiring a full Sunday closures.
Although customers will not notice any difference to their journeys at this stage, when switched on across the whole line in 2014, the signalling system will allow trains to run faster and closer together.
This will deliver a capacity increase of 20 per cent - enough to carry an extra 11,000 passengers per hour and meaning customers will benefit from more frequent and faster journeys.
David Waboso, LU's Capital Programmes Director, said: 'We are making good progress with the upgrade of the Northern line - London's busiest line. The use of the new signalling system on this first section of the line provides a good foundation for the rest of the roll out.
'Once the Northern line upgrade is completed customers will have faster, more frequent and more reliable services.
'The upgrade will mean we can carry an extra 11,000 passengers per hour which is equivalent to a fifth more passengers. Journey times will also be reduced by 18 per cent.
'We would like to thank customers who use the High Barnet branch early on Sundays for their patience while these works have taken place.'
Much preparatory work for the new signalling system has had to be done, including putting in new trackside wiring, converting the line's trains to make them compatible with the new system and training all Northern line train operators to use the new signalling system.