The railway between Three Bridges, Brighton and Lewes was closed on Saturday (February 19) and will remain shut until Sunday (February 27) as engineers work to rebuild Copyhold Junction near Haywards Heath, lay new track and shore up embankments.
Alternative train and bus services are now in place and passengers have been warned that journeys will take longer than normal.
Network Rail Kent and Sussex has shared some photos on Twitter of the huge amount of work being carried out.
“The main driver for the nine-day closure was the rebuild of Copyhold Junction near Haywards Heath with 6,000tn of ballast and 1,000m of track,” said a spokesperson.
“We can’t work here without closing all lines south of Three Bridges,” they said, adding that the only alternative to closing for nine days was 20 weekends or four bank holiday closures.
“The work was delayed from 2019 and couldn’t be pushed back any longer,” said the spokesperson.