Four Lines Modernisation

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 new system is already bringing benefits to parts of these lines. Since September 2021 journey times between Hammersmith, Stepney Green and Monument have improved by approximately 10%. We've also increased the number of trains in this area from 27 trains an hour to 28 trains an hour during the busiest times.

The original timeline for the signalling works - set out in 2015 - has been revised because of the challenges associated with a programme of this size as well as the impact of the coronavirus pandemic. We will confirm a new timeline as soon as possible.

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