Updated | New Flat Rock Creek Bridge much stronger and safer

Transport for NSW copped some flak when it closed Sir Bertram Stevens Drive in Royal National Park to replace Flat Rock Creek Bridge because of the traffic disruption, but the outcome is very positive.

The new bridge, which opened by the target date of October 20 after seven weeks of work, is a far cry from the 75-year-old timber structure it replaced.

The original bridge was built in 1945 at the end of WWII and connected Bundeena with Sutherland Shire via Audley Weir. It was badly damaged in the 1994 bushfires and needed repairs.

While the new bridge was under construction, residents of Bundeena and Maianbar had a long detour through Waterfall.

Traffic at Waterfall was gridlocked at times on Sunday afternoons, and Monday in the case of the long weekend.

While the new bridge has opened, work will continue to the end of October, with sign posting, pavement markings and slope stabilising to be completed.

Work will be carried out from 7am to 5pm Monday to Friday, weather permitting.

Motorists are advised to drive to the conditions and allow extra travel time.

Heathcote MP Lee Evans said the aim had been to replace the bridge before peak summer traffic and crews "worked around the clock" to meet the October 20 target.

The project is the third and final stage of road improvement works in Royal National Park.

Stage one involved maintenance work on Sir Bertram Stevens Drive between Garie Road and McKell Avenue, and slope rehabilitation work on McKell Avenue was carried out in the second stage.