A critical flaw in traffic modelling for Perth's Roe 8 highway extension underestimates the number of trucks that will use the road by up to 16,500 and invalidates the noise management plan and road design, new analysis has suggested.

The study, conducted for the Coolbellup Residents Association (CRA), found any higher-than-expected noise would have a significant impact on the health of residents in North Lake, South Lake and Bibra Lake.

The review of the methodology used by Main Roads and Roe 8's construction consortium was conducted by University of Western Australia (UWA) School of Physics researcher and acoustics specialist Shane Chambers.

Mr Chambers said it meant the $450 million project had been designed without the correct noise mitigation measures, and Main Roads needed to go back to the drawing board.

His findings were presented to a residents' forum in Coolbellup, where some locals expressed concern about the impact of any extra noise.

Mr Chambers said the state's Roe 8 Noise Management Plan was based on an incorrect analysis of daytime traffic and noise studies to 2031 at Roe Highway under Karel Avenue bridge.

"Such practice invalidates the entire traffic model and modelling of subsequent noise doses from the traffic," his analysis stated.

It found the modelling did not take into consideration night-time traffic and noise, even though the plan was for the highway to deliver freight 24 hours a day to Fremantle Port.

The review asserted the modelling also did not properly consider the extra trucks from across the metropolitan area which would now take advantage of Roe 8.

"The construction does not apply the correct method for a change in geospatiotemporal flow of heavy vehicles to 2031," it said.

Mr Chambers said it was the result of simple algebraic error after road freight growth figures from the Perth Urban Corridor Strategy 2007 were wrongly applied, meaning up to 16,500 trucks per day were unaccounted for.

"What I've found is there appears to be a very large miscalculation in the number of trucks that will appear on the road in 2031," he said.

"And the noise impact survey for residents doesn't take this into account unfortunately.

"It really basically invalidates the current design of the road, which is quite alarming."

He said the error would "likely cause a significant impact on health and material cost on amenity belonging to the residents".

Residents call for project to be stopped

CRA spokeswoman Alison Wright said the project should be halted until residents were given the "real story".

"Now we have this new research which indicates we might have real concerns about levels of noise on an everyday basis, which is different from what Main Roads were presenting as safe and okay for the community," Ms Wright said.

Bill Marmion says modelling suggests Roe 8 will carry 6,900 trucks on average per day by 2021. ( ABC News: Andrew O'Connor )

Transport Minister Bill Marmion did not reject Mr Chambers' claims.

But he said modelling undertaken by Main Roads in September 2015 demonstrated by 2021, Roe 8 would carry an average of 6,900 trucks between Murdoch Drive and North Lake Road per day.

There would also be approximately 74,000 light vehicles. No figures were provided to 2031.

"This modelling does not represent a marked change from the model prepared to inform the planning of Roe 8 between 2009 and 2011," Mr Marmion said.

"Final noise mitigation designs will be based on the most recent traffic modelling."

State Fremantle MP Simone McGurk said the study, if correct, showed the project had been rushed and mishandled.

"What we need is an independent evaluation of all the documents on which this project is based, and then a decision about what the best plan is," she said.