Network Rail is investing more than £2.2m to renew track in several locations between London Marylebone and Bicester.
This is to get the line in the best possible condition and ready for passengers when coronavirus travel restrictions can be eased.
The upgrades are taking place during this latest period of national lockdown - when only essential journeys are permitted – so fewer passengers will be affected by the railway closures needed for the work to be done.
As old track will be torn up and new modern railway lines laid, some routes will be shut and rail replacement bus services will be in operation instead.
Dave Penney, Network Rail’s Central route director, said: “While passenger numbers are still low, we’re making sure the Chiltern main line is in the best possible shape ready to welcome passengers back when lockdown measures are eased.
“For those who are still travelling by rail for reasons permitted by government, I’d urge people to check National Rail Enquiries before they set off on their journey so they know what to expect.”
Eleni Jordan, commercial and customer strategy director at Chiltern Railways, said: “The important track replacement work being carried out by Network Rail will ensure that we can continue to provide a safe, reliable and punctual service for our customers when restrictions on travel are eased.
Customers who need to travel during these dates should check their journey via the Chiltern website or app before starting their journey.”
Those using the rail network for essential journeys should leave more time to complete their journeys and check before travelling at www.nationalrail.co.uk or with their train operator.