Network Rail’s £81 million project to replace 12 miles of track, signalling and overhead power lines in the Watford area is due to start next month.
Work will begin on Saturday, May 3, and continue through until Monday, May 5.
All day on May 3 and up until noon on May 4 there will be no London Overground rail services running.
There will be replacement bus services running between Watford Junction and Harrow and Wealdstone every 20 minutes.
Replacement bus services will also be running between Watford Junction and St Albans City all day.
Post-noon on May 4, additional coach services will be calling between Hemel Hempstead, Watford Junction and Euston approximately every 30 minutes.
On Monday, May 5, London Overground will be in operation all day, providing a rail service between London and Watford Junction.
A replacement bus service will run between Watford Junction and St Albans City until just after midday when a normal service will resume.
London Underground will be running services to Watford Metropolitan station as normal throughout this period.
The scheme is part of the train operator’s £120 million plan to improve service between Milton Keynes and London Euston.
More work is due to take place in August.