Tolling giant Transurban warned the previous New South Wales government of potential traffic "hotspots" on Victoria Road and the Anzac Bridge more than a year before the Rozelle Interchange opened, a parliamentary inquiry has heard.

The inquiry is currently scrutinising the traffic modelling and design decisions behind the trouble-plagued interchange, which has sparked traffic chaos since opening last November.

Transurban, which owns and operates the Westconnex motorway that funnels cars through the interchange, told the inquiry it had flagged potential hotspots with the government in analysis it undertook in July 2022.

Transurban's general manager for WestConnex, Denise Kelly said those hotspots included Anzac Bridge and Victoria Road, two areas which have been among the most affected since the interchange opened.

"Those discussions did not centre on .. structural changes at that time," she said.

"However they did look at what are likely the hotspots and what we could do to alleviate that."

Transurban's head of public affairs Alisa Hitchcock was asked whether the government had ever asked the company for its opinion on whether potential traffic problems could be fixed in the design or construction of the project.

"Transurban wasn't involved in the design or the construction phase, so I think to the best of our knowledge we didn't flag design or construction challenges with Transport for NSW," Ms Hitchcock replied.

Transurban was also grilled by committee chair Cate Faehrmann about why documents related to Transburban's agreements with the government had been partially redacted in response to freedom of information requests.

Ms Faehrmann demanded to know whether there were any arrangements to prioritise Westconnex motorists using the interchange or deals to provide compensation to Transurban if the government made changes that reduced the amount of drivers using the motorway.

"There is nothing in those pages that relate to the surface road network or any kind of arrangements relating to the prioritisation or otherwise of traffic on the Rozelle Interchange and on the WestConnex network," Ms Kelly told the inquiry.

Meanwhile the joint venture that won a contract for the interchange's design and construction told the inquiry it was not responsible for issues in the design of the motorway.

John Holland's Executive General Manager for Major Projects Jim Salmon told the inquiry that Transport for NSW has created the reference design for the project and the joint venture simply delivered a detailed design that complied with that.

He said it had made "no functional changes" other than increasing the amount of parklands above the interchange.

"In terms of where the project linked in to the local road network, we comply with what is prescribed," Mr Salmon said.

When asked whether John Holland or CPB Contractors had given any advice to the former government about traffic congestion or the interchange's impact on surrounding roads, Mr Salmon said "surface traffic is the responsibility of Transport NSW."

John Holland and its joint venture partner CPB Contractors were also grilled about contaminated recycled mulch that was spread across hectares of parkland above the interchange, and revealed that it is no longer using recycled mulch after the scandal.

"We have taken a decision as a business to only use natural mulch because of the issues that have been highlighted in Rozelle," Graeme Silvester from CPB Contractors said.

Only about 40 per cent of the Rozelle parkland has been reopened, which Mr Silvester said was largely due to delays in tracking down large supplies of natural mulch.