More than 19,000 motorists a day rely on it to travel between Newcastle, the airport and Port Stephens.

But engineering reports obtained by Government Information Public Access (GIPA) legislation paint a picture of a piece of critical transport infrastructure that is showing its age.

The most recent bridge inspection report highlights vertical cracking on the piers, significant cracking on the pier aprons and metal corrosion among other issues that require ongoing attention.

The wear and tear has been compounded by the increasing volume of traffic that crosses the bridge each day.

"The bridge now needs to cater for special load limited trucks which weigh 64.5 tonnes. The frequency of these heavy loads is increasing over time," a 2020 report into a proposed $6 million step joint strengthening project noted.

Millions of dollars have been spent in the past 15 years replacing and upgrading worn parts of the structure to ensure it remains safe.

Built in 1971, the prestressed box girder bridge has an overall length of 1023 meters consisting of 23 spans.

Spans 1 to 8 and spans 15 to 23 are on land and spans 9 to 15 are in the river channel.

Two expansion joints located over the half joints of spans 11 and 13 were originally constructed using steel roller bearings. The bearings were replaced with elastomeric bearings in 2007.

In 2021, concrete cracking around the bridge girder openings caused by heavy truck movements resulted in another project to strengthen the step joints with 5mm steel plates.

Stress testing of the work in January 2022 found the work was holding up and had significantly stabilised the bridge structure.

An underwater cleaning and inspection of the bridge piers in late 2022 found numerous points of wear and tear around piers 9 to 13.

No major defects found on the piles, but large sections of steel casings missing on piles of piers 9, 10 and 11.

Pile cap curtains also showed extensive rust bleeding and cracks.

"The piles under piers 9 to 13 have areas of concrete showing where the steel casing is deteriorated and corroded away with at times large areas of concrete pile surface exposed," a contractor's report said.

"The exposed concrete surfaces on these elements are in good condition with no signs of loss of concrete matrix, rust bleeding or cracking. No washout areas exceeding 10 to 20mm of concrete surface were found during this inspection.

"As per the underwater inspection training and briefing, loss of the steel casing is to be rated as loss of a non-structural element and therefore casing loss does not influence the pile condition."

Transport for NSW undertook another project to repair the batter walls that had been damaged from ongoing stormwater scouring.

Shotcrete was used to secure the eroded area under the bridge and new drainage channels were installed.

A void was under the road was also identified and filled with grout.