The Environmental Protection Authority has vowed to investigate the impact of the Bunbury Outer Ring Road's southern section after receiving more than 640 submissions calling for a public environmental review.
The decision was made by EPA chairman Dr Tom Hatton after he determined the proposal's plan to clear 98 hectares of flora and vegetation had the potential to impact threatened ecological communities and inland waterways.
Dr Hatton also stated that the project had the ability to impact terrestrial fauna, groundwater dependant ecosystems and disturb Aboriginal heritage sites and the site's amenity.
In justifying the decision, Dr Hatton said several of the preliminary key environmental factors were "complex" and a detailed assessment was required to determine the extent of the proposal's impacts and how they could be managed.
In total, the referral gathered more than 664 submissions, more than 96 per cent of which were in favour of a review of the proposal.
The EPA will now begin an eight-week public review, gathering further information on alternative alignments and conducting surveys to confirm the impact the project could have on protected flora and fauna.
The review will also assess the environmental management plans that could be implemented to avoid and manage the impact on both the environment and the social surroundings.
The decision to review is not appealable.
Since the federal government's funding announcement in April 2018, tensions between the public and Main Roads have flared, with people unhappy with the southern alignment of the road.
Concerns included the welfare of the endangered Western Ringtail Possum and a valued large tuart tree.
The EPA announcement comes just days after 138 electors in the Shire of Capel called for a special meeting of council to request the council inform the state government that the southern portion of the Bunbury Outer Ring Road should be re-routed to avoid bisecting Gelorup.
It is understood that, under the current plan, 37 property owners would be affected and land would need to be resumed to make way for the controversial road development.
Gelorup resident and petition founder Rosina Mogg said she was pleased by the news, but said that the fight was not over.
"We're not giving up," she said.
"I understand they have called for a public submission with more information and we're prepared to do that."
Main Roads spokesman Dean Roberts told the Bunbury Mail that the project's timeline allowed for a full environmental assessment.
It is understood the Bunbury Outer Ring Road southern section has also been referred to the federal environmental regulator for a level of assessment, which is being awaited.
Main Roads' Bunbury Outer Ring Road team has been investigating two corridors for the southern section of Bunbury Outer Ring Road since mid 2018, holding a series of community consultation sessions on the plan.
The state government determined that, based on the environmental assessments undertaken to date, both alignments were likely to have similar environmental impacts.
In June, the state government announced it would proceed with planning the Bunbury Outer Ring Road's southern alignment through the existing road reserve.
More to come.