The mainline between Sussex and London will close for nine days in February as Network Rail plans a major upgrade of the track.
The track between Three Bridges, Brighton and Lewes will close for nine days from Saturday 19 to Sunday 27 February 2022.
It's part of an £11m upgrade which will see parts of the track replaced and work to build a new underpass.
Network Rail is planning an £11m upgrade which will replace 1980s track at Copyhold Junction near Haywards Heath, and between Burgess Hill and Lewes.
A new underpass to provide safe access under the railway at Hassocks will also be built.
Alternative travel arrangements will be put in place for passengers, including replacement buses and ticket acceptance on open routes.
The work will include:
Using over 7,000 tonnes of ballast - the stones beneath the track that give support
Over 1,000 metres of track renewal
Eight sets of point renewals - these are mechanical systems that move the switches and crossings that guide trains from one track to another.
Network Rail Southern region's investment director Paul Harwood said:
"We never take the decision to close the railway lightly and have reviewed this work and access approach in light of the difficult year for passengers, the industry and the country at large, to confirm it is the best option.
"As we need to get this critical work done quickly and efficiently to help the country and the railway build back from the pandemic, we believe that getting the work done in 9 days and the supporting weekends has never been more important.
Chris Fowler, Customer Services Director for Southern, said:
"This route is one of the country's busiest, and Network Rail's track renewal is essential to give our customers the reliable, on-time services they rightly expect. We'll be ensuring that alternative transport is in place, and we'll issue detailed travel advice over the coming months. Journeys will take considerably longer during the nine days of work and we thank customers in advance for their patience."