Network Rail is working on the railway between Tonbridge and Hastings through Tunbridge Wells in order to make the services more reliable for the network's passengers.
Engineers have been working on the line since December making improvements, including the installation of new signals and improving the conditions of the conductor rail equipment.
This is the equipment that provides power to trains, which has been updated to make its delivery more efficient.
Further work has also been added to increase the reliability of points, which lets trains move from one set of tracks to another.
Continuing changes are being made in the evening and, as a result, trains leaving London and Hastings are receiving replacement bus services.
Paul Rutter, Network Rail's area director, said: "We are always working to improve the reliability of the railway as part of our Railway Upgrade Plan and by continuing this scheme, we can continue to tackle some of the root causes of delays for passengers."