Heathcote Road will be closed on some weeknights and weekends as work on the Woronora River bridge upgrade begins.
The project is expected to take 12 months to complete.
The state government originally planned to widen the existing bridge and access roads, but after a response from the community, it announced a week before Christmas 2021 that a second bridge would be built to separate traffic.
However, each bridge only has one lane.
The new bridge will be on the upstream side of the existing bridge and will provide one lane for westbound traffic, while the existing bridge will be modified to provide one lane for eastbound traffic.
Transport for NSW said excavations and rock excavation on some weekday evenings and weekends would require Heathcote Road between New Illawarra Road and Princes Highway.
“These are expected to start in May 2022, weather permitting, and will be between 8 p.m. and 5 a.m.,” a statement said.
“The weekend closures are expected to begin in early June, weather permitting, and will take place between 8pm Friday and 5am Monday.
“During weekend closures, there will be 24-hour construction to reduce the need for set-up and tear down and reduce the number of closures generally required to deliver the project safely.
“Transport will notify the community when specific closing dates have been completed, closer to time.”