Engineers are pictured hard at work at Wivelsfield railway station.
The work is part of a £67million upgrade of the Brighton Main Line.
Great progress has been made Burgess Hill this week, Network Rail has said, with engineers laying new conductor rail.
Drainage works at Haywards Heath are also being carried out as part of the improvements. A new track is also being laid at Balcombe.
Network Rail is carrying out major engineering works on the Brighton Main Line – closing the line between Three Bridges and Brighton and Three Bridges to Lewes for nine days.
No direct trains will run between Three Bridges and Brighton and Three Bridges to Lewes until February 24.
Rail replacement buses are in operation, but journey times are expected to take an hour longer than usual.
The closure affects services to and from Hassocks, Burgess Gill, Wivelsfield, Haywards Health and Balcombe.