Rail commuters have been warned to expect major disruption to services in August.
London Midland train services will terminate at Hemel Hempstead over three weekends, with replacement bus services to Bletchley, Milton Keynes, and beyond.
Work will take place on the following dates:
Saturday, August 9 - Monday, August 11;
Saturday, August 16 - Monday, August 18;
Saturday, August 23 - Tuesday, August 26.
The work is part of an £81million investment to improve reliability and punctuality on the West Coast Mainline by Network Rail.
Virgin Trains willl also be affected, with intercity services that call at Milton Keynes instead being diverted along other routes.
Rebecca Freeman, London Midland project manager for the Watford Area Renewals Programme, said: “We know that the closures will affect many people’s travel plans and we’d like to thank our customers in advance for their patience and cooperation.
“During the closures journey times will be extended and will involve various changes. I urge passengers who need to travel to check in advance and plan their journey.”
London Midland is also advising passengers to consider making alternative work or travel arrangements on August 11 and 18, as there will be a reduced train service into London on these days.
Ms Freeman added: “Those two days provide an opportunity to take advantage of flexible working or annual leave, especially as it’s the school holidays. We wanted to let our customers know about the reduced service now, so that they have plenty of time to make arrangements.”