The 144-year-old Windsor Bridge in Sydney's northwest is a risk to public safety, authorities say, but structural engineers argue the "old lady's legs are in fine form".
The historic bridge - built in 1874 for horse-drawn vehicles - is slated for demolition and the NSW government plans to build a replacement bridge and connecting road to Windsor's historical Thompson Square.
But bridge engineers believe the existing structure can be repaired and kept for use by local traffic while a bypass is built on the outskirts of the town to meet traffic demands.
The Roads and Maritime Services told an NSW upper house inquiry on Monday replacing the bridge was the best option for the community, claiming any bypasses were not feasible.
RMS north west precinct director Colin Langford said the structure was deteriorating and posed a risk to public safety.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"There are concrete chunks falling off this bridge," Mr Langford said.
"(It) doesn't meet current standards."
But two retired bridge engineers who have been involved in some 1200 bridge projects say its destruction would deprive NSW of "one of its most historical treasures".
Brian Pearson and Ray Wedgewood, who have a combined experience of 80 years in the industry, told the inquiry destroying the bridge was unnecessary.
"The grand old lady's legs are in fine form .... It is wrong and unnecessary to destroy a bridge that is in good condition and has serviced the community for 144 years," Mr Pearson told the inquiry.
Engineer Peter Stewart conceded the beam bridge which spans the Hawkesbury River needed repair but suggested it could be upgraded.
"I've been involved in strengthening the Harbour Bridge where the RMS invested significant funds and it now has a very long lifespan," he told the hearing.
"This one seems to have slipped through ... they don't seem they want to keep it."
The project, which was first flagged in 2008 and has already gone to tender, is facing delays after the RMS discovered historical artefacts nearby including a brick barrel drain from the early 1800s.
The replacement project has already cost about $30 million, before construction has even started, out of its $50 million estimated total cost, the inquiry chaired by Shooters MP Robert Brown heard.
Mr Brown has written a letter to Roads Minister Melinda Pavey requesting the government defer the tender process until the inquiry reports on its findings.
