The Gilford Road will be closed over the weekend to facilitate a sewer connection for a new housing development.
It will be closed from 6.30pm on Saturday night until midnight on Sunday from Lower Toberhewny Lane to Willowtree Manor (opposite Upper Toberhewny Lane).
Two diversions will be in place.
The first, for southbound traffic will be via Banbridge Road, Waringstown Road and Dunkirk Road.
The second, for northbound traffic is via Deans Road, Sugar Island Road, Monbrief Road, Tandragee Road, Russell Drive, Malcolm Road, Queen Street and Flush Place.
The work is being carried out by NI Water.
They estimate the delay to motorists will be in the region of five to 15 minutes.