New signalling has begun operation across the London Underground Circle, District, Hammersmith and City and Metropolitan lines and will increase frequency in central London from 28 to 32 per hour when complete.
This will lead to a capacity increase of a third on the four lines, equivalent to the space for an extra 36,500 customers during peak times. The frequency increases will only be introduced from 2021, however, with the project targeted for completion in 2023.
This first section of the new Thales signalling system covers nearly half the Underground.
The system is currently operating between Hammersmith and Latimer Road, the first part of the network to benefit from the improvements.
A new, signal control centre at Hammersmith is already operational, and the new S-stock Tube trains have been running exclusively on the four lines since 2017.
Shaun Jones, VP, ground transportation systems, Thales, commented: 'The successful introduction of this section is a significant step on the journey to upgrade the signalling system of this highly complex railway.'
'Although there is a chance of some short delays on the Circle and Hammersmith & City lines as the new system gets underway, so far it has been working well,' TfL said in a statement.
The modernisation of the four lines means some of the oldest equipment on the Tube network will be replaced, including a signal box at Edgware Road that was built in 1926.
The lines carry a combined 1.3 million customers per day, all of whom are already benefitting from the new, walk-through, air-conditioned trains that were introduced for the first time in 2010.