KiwiRail teams will return to work on Auckland's Western Line in March as they seek to complete rebuilding a series of tracks on the rail network.
Sites between Newmarket and New Lynn will be worked on from March 10 through to early May.
"Between 11 March and 24 April, trains will only be able to run on one of the two tracks while the other is being worked on," KiwiRail said.
"Over this period trains will run on a revised schedule - every 20 minutes throughout the day and every 30 minutes in the evening."
Auckland Transport's director of public transport and active modes, Stacey Van Der Putten, said "we do expect there will be times when services are very busy, especially during the morning peak when both workers and students are travelling at the same time".
To manage the demand, the western line service will have six carriages at peak times and there will also be additional buses running.
Work on the Rail Network Rebuild began over Christmas during a network-wide shutdown when trains weren't running.
Much of the invasive work was completed but they now need to "finish the job".
The announcement comes after a turbulent February for Auckland Transport where high temperatures and track issues were blamed for a swath of train cancellations.
KiwiRail chief asset development officer David Gordon said the Rail Network Rebuild "is removing the need for heat and temporary speed restrictions, which slow down commuter trains now".
The work is also necessary if the rail network is to keep up with the increasing frequency of trains that will arise once the City Rail Link is up and running.
Work under the Rail Network Rebuild includes drainage improvement work, replacing ballast (the stones the tracks sit in), and replacing sleepers and rail when necessary.
Gordon said most of the work will be done at night and on the weekends, but some work will need to be done during the day.
"In previous Rail Network Rebuild stages we have had to close sections of the network for months at a time. We have been able to avoid this high level of disruption for the Western Line work, but we do appreciate that reduced services are an inconvenience for commuters," Gordon said.
"We continue to be grateful for our customers' patience and flexibility," Van Der Putten said.
She also pointed out that of the seven weeks of disruption, two weeks will be school holidays when things will be quieter.
During the work, buses will stop at all stations between New Lynn and Newmarket every 10 minutes from 7am until 8:30am on weekdays.
There will also be more buses on the 22N route, which connects Western Line stations between New Lynn and Kingsland with the city centre.
KiwiRail is in ongoing discussions with the Government about securing funding to complete the rest of the Rail Network Rebuild across Auckland which would focus on the western line past New Lynn, and further foundation replacement work on the southern line south of Ōtāhuhu.
