Network rail has confirmed the details of a £13m investment to improve the track between Southport and Wigan.
Work will start on the week beginning August 12, with the majority due to be completed by December.
Most of the work will take place overnight when trains are not running, but there will be some impact on late evening services Monday to Thursday.
Martin Frobisher, Network Rail area director, said: “The investment we are making will provide a smoother ride and a more reliable service for passengers travelling between Southport and Wigan.
“The track here along this route is extremely old and was beginning to have an adverse affect on train punctuality.
“We’ll be replacing more than 11 miles of track which will allow more trains to run on time along this important route.”
The line passes from Southport through Meols Cop, Bescar Lane, New Lane, Burscough Bridge, Hoscar, Parbold, Appley Bridge and Gathurst on its way to Wigan Wallgate, where passengers can change for Manchester Airport.
Details of amended services will be available on Northern Rail’s website, www.northernrail.org, by the end of the week.