IMPROVEMENT work to the northern section of the Metropolitan Line will begin on Saturday (August 19).
Some of the oldest track on the network will be replaced at 16 sites between Amersham and Moor Park.
The work will be carried out on five weekends between now and Christmas, during which tracks will be closed and services and suspended.
Met Line general manager Angela Back said: "This work will bring noticeable changes to the service, with passengers soon benefiting from a quicker and more reliable service.
"These essential works have been timed to cause the minimum disruption to passengers and we ask them to bear with us, but check before they travel at the weekend.
During the closures, there will be no Met Line services between Moor Park and Amersham; Chalfont and Latimer and Chesham, and no fast services north of Harrow-on-the-Hill.
An all-stations service will continue to operate to Watford.
A bus service will operate along the affected route.
Chiltern Railways services between Marylebone and Aylesbury via Amersham will also be suspended, with customers advised to use the service via Princes Risborough instead Closures are also planned for the weekends October 7 and 8; November 11 and 12, and December 9 and 10 and 16 and 17.
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