The railway between Guildford and Petersfield will be closed for one week from Sunday, October 21 to Saturday, October 28, with a bus replacement service in operation.
Network Rail engineers will begin around-the-clock-working to update the 1970s signalling equipment between Farncombe and Petersfield, as part of the wider Portsmouth Direct Upgrade programme.
The aim is to create more reliable and safer level crossings, reduce journey times, and open up the potential for more train services in the future.
Mark Killick, Network Rail’s Wessex route director, said: “Next month our engineers will continue key upgrades to track, signalling and level crossings between Farncombe and Petersfield, as part of our wider Portsmouth Direct Upgrade.
“This work is crucial to improving the reliability of the railway for customers travelling between Portsmouth and London Waterloo and will help reduce journey times as well as provide the opportunity to increase the number of service in the future.
“There is never a good time to close the railway but our engineers will be making use of every minute to complete a wide range of work and we’re grateful to customers for their patience and understanding during this time.”
Peter Williams, South Western Railway's customer and commercial director, said: “Customers should please check before travelling and allow extra time for journeys, as buses are replacing trains between Guildford and Petersfield for nine days from Saturday 21 to Sunday 29 October, extending to Rowlands Castle and Havant on Sunday 29 October.
“Making the decision to close parts of the network is really difficult because we know how inconvenient it can be for customers, but giving Network Rail this access will allow them to make significant progress upgrading the line and help avoid future day-to-day disruption.
“We thank customers for their patience as these essential upgrades are carried out, which when complete will boost reliability for many years to come."