Three Bridges station car park will be closed for almost a month as it will be transformed into a 'bus hub' ahead of railway works.
Network Rail said the car park closed just before midnight on Friday, February 8, and it will reopen at 6am on Monday, March 4.
Alternative parking is being provided for season ticket holders at Gatwick Airport.
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The car park will be used as a rail replacement bus station during Network Rail closures of the Brighton Mainline.
There will be a nine-day closure of the line between Brighton/Lewes and Three Bridges from Saturday, February February 16 to February 24.
This means no trains will run between the stations.
Rail operator Govia Thameslink Railway (GTR) said it is diverting what services it can and is laying on a rail replacement bus service.
It added that Three Bridges station car park will be turned into a 'bespoke bus hub', with toilets, a customer information point, refreshments and extra staff on hand to help passengers.
Keith Jipps, GTR’s infrastructure director, said: “While we are putting on over 200 rail replacement buses and bringing in hundreds of additional staff, I’d urge passengers to consider alternative routes, working from home if possible or travelling outside the rush hours. It will take much longer to make your journey with travel times extended by as much as one hour.
“The train via Littlehampton is the best alternative to and from Brighton and for other journeys we’ll have buses and coaches in circulation every day on nine core routes, many of them connecting with a dedicated bus hub at Three Bridges.
“While we will be very busy travelling to and from Three Bridges and London at peak times, there will be less demand for trains and buses to the coast and Brighton.”
The closures are part of a £67 million upgrade of the Brighton Mainline.
Network Rail said the work will renew and upgrade track junctions and signalling, shore up embankments to reduce the risk of landslides and introduce new technology that not only detects potential problems before they occur, but can help the railway recover faster if there is a fault.
There is also extensive work within four Victorian tunnels to stop leaks and drainage issues, which have caused significant delays for passengers in the past.
John Halsall, managing director, Network Rail South East route, said: “This work is absolutely critical as this stretch is one of the most unreliable parts of the network, accounting for half the delays to trains arriving from the south into central London.
“We know it’s never a good time to close the railway, but the only alternative would have been to close the line for 84 weekends over the course of two years.
“Doing the work over this nine-day period means we can achieve so much more and deliver the punctuality and reliability benefits to passengers much sooner, plus the railway is much quieter during the school holidays.
“Working with our colleagues at Govia Thameslink Railway, we are making every effort to enable those passengers who need to travel during this period to do so comfortably.”