The lines between Three Bridges and Lewes and Three Bridges and Brighton are closed today due to engineering work.
Rail replacement transport is scheduled to run between the stations but a reduced bus service will be calling at Wivelsfield due to road closures in the area, Southern Rail said.
This is expected until the end of the day.
Trains are still running between Lewes and Brighton according to National Rail.
Most Southern and Thameslink rail replacement buses will not be able to serve Wivelsfield today, Southern Rail said.
A spokesman added: “A smaller bus will need to operate a shuttle service between Burgess Hill, Wivelsfield and Haywards Heath due to road closure restrictions. These shuttles will operate in both directions.
“Please leave extra time for journeys to and from Wivelsfield. You may wish to consider using Burgess Hill as an alternative bus pick-up and drop-off location.
“Tickets for Wivelsfield will be accepted at Burgess Hill instead.
“Shuttle buses will be departing from Burgess Hill at 30 minutes past the hour, from 6.30am onwards. These buses will call at Wivelsfield and Haywards Heath.
“Shuttle buses will be departing from Haywards Heath on the hour, from 7am onwards. These buses will call at Wivelsfield and Burgess Hill.”
The shuttle bus service is initially being provided by Big Lemon buses, he added.
The spokesman said: “If you are travelling from Wivelsfield and heading further than Burgess Hill or Haywards Heath, you will need to change buses.
“If you are on a bus which started its journey at Brighton, Three Bridges or Plumpton, your bus will not call at Wivelsfield, and you will need to change buses at Burgess Hill or Haywards Heath for the shuttle service.”
As part of the engineering works causing today’s closure of the railway lines in the area, the road over the level crossing on Junction Road (Wivelsfield) is also closed, according to the rail operator.
This means that the larger buses and coaches on our scheduled bus services will need to take an alternative route, and will not be able to access Wivelsfield, as the remaining roads are not suitable.