Trains between Three Bridges and Haywards Heath may be subject to delay this afternoon due to a fault with the signalling system, Southern has said.
Network Rail engineers are looking into the issue and platform changes are likely at Three Bridges station.
Passengers are advised to check station information screens, listen out for station announcements and check the journey planners prior to travelling.
Some trains at Three Bridges will have the following platform alterations:
All trains towards Crawley and Horsham will depart from platform 3.
All Thameslink only trains towards Bedford will depart from platform 4.
On the Southern website a spokesman says: “The fault has been traced back to a ‘Track Circuit Failure’ which means the signalling system is unable to automatically detect whether or not the next section of track is clear.
“To work around this, train crew can either liaise with the signaller gaining their authority to continue or divert via alternative lines.
“Due to the high volume of trains passing through this area, a decision has been made to divert trains, as this is the quickest option, causing fewer delays to the train service.”