Network Rail is set to close the railway line between Falmer and Polegate for four days next week.
There will be no trains via Lewes from Thursday, March 7 to Sunday March 10 as Network Rail engineers work to replace old signalling equipment with 'modern, more reliable technology'.
Here's all you need to know.
Which routes are affected?
During the closure, there will be no trains between the following stations:
Wivelsfield - Lewes
Falmer - Lewes
Seaford - Lewes
Polegate - Lewes.
This means there will be no direct trains between Brighton and Eastbourne.
There will be a rail replacement service running between affected stations.
What is the travel advice?
Southern Rail told passengers: "If you do wish to travel, we will ensure that you can, but please note you will need to allow extra time for your journey."
It told people to consider working from home or travelling outside of peak time. It said people should allow more time to travel.
The rail operator added that non-folding cycles cannot be carried on replacement buses
For those who require assistance, book in advance at southernrailway.com/accessibility
What about travelling between Brighton and Falmer?
For the Brighton to Falmer route, there will be a shuttle train replacing normal service, running every 40 minutes
It will call at London Road (Brighton) and Moulsecoomb.
Which bus services are in place for areas with no rail service?
A regular bus service has been arranged connecting with trains at Polegate, Haywards Heath, Brighton and East Grinstead.
Ticket acceptance will also be valid on local bus services:
28 and 29 (Lewes to Brighton)
12 (Brighton to Eastbourne)
25 (University Bus to Falmer)
Click here to plan your journey
Will it affect journeys between Eastbourne and Hastings?
Southern Rail said an amended timetable will be in operation throughout the four-day closure.
On Thursday March 7 to Friday March 8, customers travelling to/from Central London may travel via St Leonards Warrior Square on Southeastern services where tickets will be accepted.
What about trains between London and Coastway West stations (Littlehampton, Bognor Regis, Portsmouth, Southampton)?
Southern said some trains will be shorter than usual due to engineering works taking place, blocking the line to where the trains are held.
What are the different replacement bus routes?
There will be a stopping bus service between Brighton and Seaford calling at London Road, Moulescoomb, Falmer, Lewes, Southease, Newhaven Town, Newhaven Harbour, Newhaven Town and Bishopstone
A stopping bus service will run between Brighton and Polegate calling at Lewes.
A limited bus service will run between Haywards Heath to Polegate, calling at Cooksbridge and Lewes.
There will be a stopping bus service between Haywards Heath and Lewes calling at Plumpton.
A limited stopping bus service with run between Lewes and Polegate calling at Glynde and Berwick
And there will be a bus service between Polegate and East Grinstead.
Are there any changes to car parking arrangements?
Part of the car park at Polegate station will be closed for buses, as will the Lewes forecourt, Haywards Heath forecourt and East Grinstead’s pick up and put down area. There will be traffic management in place for Lewes and Haywards Heath, Southern Rail said.
Those with car park season tickets to stations that have no trains will be able to use alternative car parks including Three Bridges, Haywards Heath, Brighton and Uckfield.
Why are there closures?
Network Rail said it is replacing old signalling equipment between Lewes and Seaford and replacing it with modern, more reliable technology as part of a multi-million-pound upgrade.
To find out more, visit: networkrail.co.uk/lewes