London Underground's 90-year-old signalling cabin at Edgware Road station is to be replaced with upgraded technology to enable trains to run more frequently.
The Railway Heritage Designation Advisory Board has recognised the signalling cabin as an item of historic national interest. The cabin's original technology was made in 1926 and is operated by the Metropolitan Railway.
It has a mechanical ‘K-style’ lever frame that operates the interlocking of signals and points at the complex junction used by the Circle and Hammersmith & City lines.
London Underground managing director Mark Wild said: "Upgrading the Circle, District, Hammersmith & City and Metropolitan lines will enable us to increase capacity for millions of our customers.
"When the Edgware Road signalling cabin is honourably retired as part of our modernisation programme, it will have been in use for nearly a century."
The technology is expected to reduce journey times and also deliver a 33% improvement in capacity on the four lines by the early 2020s.
London Underground design and heritage manager Mike Ashworth said: "This unique signalling cabin harks back to the earliest days of London's transport network, being originally built and used by the Metropolitan Railway in 1926.
"Ensuring we understand and preserve the heritage of the world's first underground railway, with all its surprising historic quirks, is key."
New signalling equipment installation has already started on track between Edgware Road and Hammersmith.
Global transportation systems provider Thales is providing the system, which will be installed in sections across the four lines between now and 2021.
Main benefits are being delivered by 2022 and the frequency of trains running during peak periods is expected to increase to 32 trains an hour in central London.