Because these lines share a lot of track and infrastructure, they are being modernised under a single combined and integrated project, Four Lines Modernisation (4LM).

Progress so far

A fleet of 192 modern, air-conditioned, walk-through S-stock trains now runs across the Circle, Hammersmith & City, District and Metropolitan lines.

We've also made progress on installing a new signalling and control system.

The area where the new signalling system operates (as of March 2023) covers 62 stations and 4 complex junctions (Baker Street, Aldgate, Earls Court and Edgware Road) along 62km of track, including the full Circle and Hammersmith & City lines and the east end of the District line.

The new system is already bringing benefits to parts of these lines:

  • In September 2022 we introduced a new timetable which has improved journey times by around 5% on average on the Circle and District lines between Monument, Fulham Broadway, Barons Court and Paddington
  • Since September 2021 journey times between Hammersmith and Aldgate have improved by approximately 10%. We've also increased the number of trains between Baker Street and Aldgate from 27 trains an hour to 28 trains an hour during the busiest times

Areas still to go live with the new signalling system include the Metropolitan Line north of Finchley Road and sections of the District line from Barons Court to Stamford Brook and Fulham Broadway to East Putney.

The next section to come into service will be on the Metropolitan line between Finchley Road and Preston Road in 2024.

The four lines

The four lines are among some of the oldest sections of the Underground network, with parts dating back to 1863. Together they make up 40% of the Tube network.

Some equipment used on these lines is old and needs to be replaced. We're introducing new technology that will reduce journey times and make it possible for us to run more trains..

This project will require some line closures. Stay up-to-date by checking our TfL Go app or Journey Planner and sign up to our email alerts.

New trains

The trains now in use are longer and more spacious than the old trains they replaced. The train doors are also bigger, creating extra space for more people to get on and off at stations. This speeds up journeys.

The trains also have improved audio and visual information, dedicated wheelchair spaces and colour-contrasting interiors.

New track and drainage

We will make journeys quieter and smoother by replacing old and worn out track and points. New drainage systems will make the track much less likely to flood during bad weather - this will reduce delays to journeys because of signal failures and mean fewer closures for maintenance and repair works.

New signalling system

Work to install a new signalling and control system began in summer 2016. This will eventually allow the trains to be driven automatically, with a train operator in the cab to open and close the doors. The train operator will be responsible for managing customer information and safety.

Similar technology introduced in recent years on the Jubilee and Northern lines improved performance. The new signalling system allows trains to be run closer together, meaning a more frequent service and shorter waiting times, allowing more people to be carried. This new technology will enable us to reduce delays and improve reliability.

The programme will make it possible for us to operate 32 trains an hour in the central section. Installation work will require some line closures.


  • Air-conditioned trains, with brighter more spacious interiors, low floors and dedicated spaces for wheelchair users, CCTV and other improved features
  • Space for more customers
  • Faster journeys and reduced waiting times
  • Fewer delays as safe but obsolete equipment - dating back to the 1920s in some places - is replaced with modern, computerised signalling and control systems. This equipment will be more reliable and cheaper to maintain
  • Better live customer information on platforms and to smart devices