The NSW government's plan to knock down and replace a 144-year-old bridge in Sydney's northwest will go ahead despite a parliamentary inquiry recommending the bridge be preserved.

The NSW upper house inquiry, chaired by Shooters MP Robert Brown, found “multiple deficiencies” in the $100 million Windsor Bridge replacement project.

While it didn’t recommend the project be scrapped, it did urge the government to keep the existing bridge.

The historic two-lane bridge – built in 1874 for horse-drawn vehicles – is slated for demolition with the state government planning to build a replacement bridge 35 metres downstream and a connecting road to Windsor’s historic Thompson Square.

But the inquiry, in its final report released on Wednesday, recommends the existing bridge be retained for “pedestrian, cycling and light vehicle use”.

It also urged the government to work with heritage experts to minimise the impacts on the state heritage-listed Thompson Square.

“(The committee) behoves the NSW government now, as a matter of urgency, to ensure that as much of the natural, the built and cultural heritage of the Windsor Bridge site is preserved,” Mr Brown said in a statement.

The inquiry raised concerns about the “sharp escalation” in costs over the life of the project – which in 2012 was slated to cost $50.4 million and is now estimated at $101 million.

The NSW Roads and Maritime Services insists the three-lane replacement bridge will improve traffic and safety for motorists.

It says parts of the existing bridge are “deteriorating substantially” with the structure reaching “the end of its economic life”.

The RMS on Wednesday said it was standing firm in its decision to knock down the existing bridge and build a replacement one.

Liberal MP Scot MacDonald said if the project was further delayed it could result in restricted use of the bridge and if construction was stopped it would be a “disaster” for the region.

Labor MPs Daniel Mookhey and Peter Primrose in their dissenting statement called for the project to be halted immediately.

Local group Community Action for Windsor Bridge says while the report validates the project’s issues the group is “extremely disappointed” it doesn’t call for an immediate cessation of works.

By Dominica Sanda