The railway between Leamington Spa, Banbury and Bicester is to close for nine days this summer as part of a £76 million upgrade.
Network Rail and Chiltern Railways are to close the line from July 30, reopening on August 8.
Engineers will be upgrading the signalling through the Banbury area, which will be controlled from the West Midlands Signalling Centre in Birmingham.
Work had already taken place in 2015 during planned Sunday closures and on Christmas Day and Boxing Day.
There will also be a change to the track layout in Banbury Station and the installation of infrastructure for a depot south of Banbury, which is currently being built to provide maintenance for the Chiltern Railways train fleet. Parts of this depot will open later this year.
It is hoped the investment will help improve the punctuality and reliability of train services on the Chiltern main line.
Sheila Gover, from the Cherwell Rail Users Group said the upgrade was welcome, but questioned why the railway line needed to be closed for so long.
She said: “We are astonished it needs to be closed for so long. It is going to be quite difficult because it means lots of replacement buses will be running from Leamington Spa to Banbury and Bicester.
“It is a major project. We are grateful for the upgrade because it means signalling intervals on the track will be shorter, trains can come down the line more frequently and there will be more services for users.”
Liam Sumpter, area director for Network Rail, said: “This £76m investment is key to modernise the railway through the Banbury area to provide passengers with a more reliable and modern railway.
“There is never a good time to close the railway for this length of time – and we have looked at all options and worked with Chiltern Railways to complete this work to cause the least disruption to passengers.
“More information will be released in the coming months to give passengers with all the information they need to plan their journey.”
Dave Penney, managing director at Chiltern Railways, added: “The work at Banbury is an important investment to improve the infrastructure so we can keep our trains some of the most reliable in the country.
“We are working hard to provide our customers with a step-straight-on replacement bus service to make the closure as easy as possible. We will be releasing more information on the nine day closure timetable in the coming months.”
The £76 million investment is part of Network Rail’s Railway Upgrade Plan which is seeing more than £35 billion invested in the railway until 2019.
For more information about this project, visit www.chilternrailways.co.uk/banbury-upgrade