Upgrade works to improve the railway in Cornwall will continue from Monday March 1 affecting rail services between Plymouth and Cornwall.
A replacement bus service will be in place between Par, St Austell and Truro.
Phase one of the works will see Network Rail undertake bridge replacement and track renewal work in the St Austell area from Monday March 1 to Friday March 5, and will affect services on the main line between Plymouth and Penzance.
Where the main line remains open, an amended train service will operate, with roughly one train per hour in each direction.
During phase two, Network Rail will replace a bridge in the Lostwithiel area over a series of weekends from Saturday March 13 to Sunday March 28.
During the works, buses will replace trains between Plymouth and St Austell on the weekends of March 13-14, 20-21 and 27-28.
Train services will continue to operate between Plymouth and Penzance on weekdays but train times will be amended.
Where buses replace trains, journey times will be extended by up to 50 minutes and some train departure times will also be changed to allow connections onto replacement buses, and passengers are advised to check beforehand.
Branch line services to Gunnislake and Looe will also be replaced by buses on the weekends of 20/21 and 27/28 March.
Mark Chorley, GWR Regional Station Manager, West, said: “This work is important to ensure we can continue to provide services that people can rely on at this time and we thank customers for their patience in advance.
“We have been working hard to make sure that people can be confident to travel safely, and that includes running as many trains and carriages as we can to make extra room, and replacement buses where trains cannot operate, as well as enhanced cleaning and social distancing measures.”
Michael Clapham, Network Rail’s project manager, said: “We thank passengers in advance while we carry out these vital upgrades across Cornwall and remind them to check before they travel.
“The improvements represent further investment in the reliability of the railway in Cornwall following recent signalling and track upgrades in the South West.”
GWR is operating a reduced timetable during the latest national lockdown and customers should follow Government guidelines, only travelling for work if essential or for other legally permitted reasons.
To find out more please visit: gwr.com/safety.