The widening of Armadale Road will begin next month.
Construction of the Armadale Road duplication, which is designed to reduce traffic congestion and improve freeway access, will begin early March.
The creation of a dual carriageway will impact about seven kilometres of Armadale Road between Anstey Road and Tapper Road.
A major intersection upgrade is also planned for the Nicholson Road intersection, where the traffic lights will be replaced by a roundabout, and an Armadale Road overpass built across the intersection.
The Wright and Liddlelow Roads, and Ghostgum and Rossiter Avenue intersections at Armadale Road will each be upgraded with new roundabouts.
The widening will cost about $145 million, funded jointly by the Federal and State Governments.
A pedestrian-cyclist shared path will also be built on the northern side of Armadale Road, and an underpass to connect native animals to bushland on either side of the road near William Skeet Oval is being considered.