The State Government has bought the first two of 36 parcels of private land needed to build its $1.12 billion Swan Valley bypass road.

The two Bullsbrook properties - in Warbrook and Raphael roads - cost $1.12 million.

Their sale was confirmed this month in answers to parliamentary questions, with the Government saying that negotiations were continuing to acquire more land from another 34 owners.

A spokesman for Main Roads saiq the estimated cost of acquiring the properties was about $21 million.

The Swan Valley bypass, also known as NorthLink WA or the Perth to Darwin Highway; is jointly funded by the Federal ($756 million) and State ($362 million) governments.

It involves a new 37km link from the intersection of Reid and Tonkin highways to Muchea.

It allows trucks to bypass the Swan Valley tourist stretch along Great Northern Highway

The project also includes new Tonkin Highway grade separations at Benara Road, Morley Drive and Collier Road.

The Main "Roads spokesman said most of the required private land was rural properties between Maralla Road (north ofEllenbrook) and Muchea (west of Great Northern Highway).

One property near Ballajura was also needed, bringing the total amount of land required to 185ha.

"Main Roads has worked with landowners over the past 8-10 years in determining land requirements and impacts to properties for the project," the spokesman said.

All the other land required to build the bypass was already owned by the State or Federal governments.

Work on the bypass road is due to begin next year, with the completion listed for 2019.

In State Parliament last year, Transport Minister Dean Nalder said the bypass would relieve traffic pressure on Great Northern Highway and improve congestion on West Swan Road and Lord Street.