The Four Lines Modernisation (4LM) is a series of projects by Transport for London (TfL) to modernise and upgrade the sub-surface lines of the London Underground: the Circle, District, Hammersmith & City and Metropolitan lines. The upgrades entail new rolling stock, new signalling and new track and drainage.[1][2]
- ^ "Four Lines Modernisation". Transport for London. Retrieved 2022-05-11.
- ^ "THIRD TIME LUCKY FOR SUB-SURFACE RESIGNALLING". www.modernrailways.com. 1 December 2022. Retrieved 2023-04-30.
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