Thousands of commuters face disruption on rail journeys between the Fylde coast and Manchester when a six-week engineering project begins.
Trains will be diverted around the work to electrify the track at Chorley, while others will use rail replacement buses to get passengers from Preston to Chorley.
The work, part of Network Rail’s £1bn investment in the North West, will run from July 19 until August 31.
First TransPennine Express services to Manchester Airport will be slightly reduced and run to an amended schedule. They will divert around Chorley and will not call at Horwich Parkway, Chorley or Buckshaw Parkway.
Northern Rail, which also runs services to Manchester, has yet to announce its timetable for the duration of the works. However, it is expected to feature reduced services between Chorley and Manchester Airport, making use of rail replacement buses.
The company said it has tried to keep disruption to a minimum.
Around 21,000 passengers commute from the Lancashire area to Manchester and Merseyside every day.
A spokesman for Network Rail said: “As part of more than £1bn of investment in the railway in the North West, we will be closing the railway in the Chorley area to install equipment to electrify the railway, including through the Chorley Tunnel, which will require significant changes to accommodate the overhead line equipment.
“A number of bridges will have to be rebuilt or modified and the work cannot be completed while trains are running.
“The closure has been carefully planned to keep it as short as possible and we are working closely with the train operators regarding the amended services and disruption.
“Passenger communication regarding the closure has started and further details will be released as soon as they are available. Passengers should plan their journeys and check with National Rail Enquiries before travelling.”
More details about the impact of the closure are expected over the next couple of weeks.
A spokesman for Northern Rail said efforts have been made to keep trains running where possible, rather than rely solely on rail replacement buses, for the benefit of commuters.
The spokesman added: “There will be a reduced frequency service from Chorley to Manchester.
“To make this more customer friendly, what we are doing is running a reduced train service so people can still go back and forth.”