Work to prepare the Bussell Highway dual carriageway between Busselton and Capel is expected to start in June after the start government allocated $4 million to align the area with fill.
The funds will be drawn from Main Roads minor works budget for forward works.
Due to land in the area being previously mined from mineral sands, sub-soil conditions were weak, and the compaction process would take about a year before road construction could safely proceed.
The state government is also proposing to roll the Bussell Highway duplication project into the wider Bunbury Outer Ring Road to save taxpayers money and allow works to start sooner rather than later.
However, widening the scope of the BORR project to include the Bussell Highway required agreement of the Commonwealth, and this would not happen during the election period.
The Bussell Highway duplication is planned to be delivered in two stages, with the $4 million to cover early works between the Capel bypass and Hutton Road.
Transport Minister Rita Saffioti said the Bussell Highway duplication had been undergoing planning, land acquisition and environmental processes, and they were now excited to be the first government to set the foundation for the upgrade to proceed.
"Locals and regular visitors to the South-West would be familiar with the dreaded bottleneck where the road narrows to one lane, which is badly exacerbated on long weekends," she said.
"Since coming to office, the McGowan Government has consistently publicly called for Commonwealth funding towards this important project following the previous Liberal-National government's failure to deliver the upgrade despite nearly nine years in office.
"We are now getting on with the job, and will be optimistically working with the next Federal Government to allow the project to rolled into the wider Bunbury Outer Ring Road project."
Vasse MLA Libby Mettam welcomed the announcement and said while it was only a small part of the $80 million in total needed to upgrade the 17 kilometre section of the highway, it was a step in the right direction.
There were 59 crashes on the highway between Busselton and Capel between January 2016 and December 2018, three of which were fatal.
This stretch of highway was also identified by the RAC as the riskiest road in WA and the number one priority for funding.
From March 2018 to March 2019, almost 13,000 vehicles travelled on the stretch of highway every day, with a peak 21,116 on March 1 this year.
City of Busselton mayor Grant Henley said the commitment to commence works was welcome news.