MAIN Roads WA says an unexpected delay with the beam construction process means the Muchea South Rd detour is now planned for late February or early March.
A Main Roads WA spokeswoman said a Muchea South Rd detour was necessary to enable bridge beams to be installed safely over the road, which could not be done over live traffic.
She said once the Muchea South Rd detour was completed it would be followed by the Brand Hwy detour.
Twenty-four beams beams will be installed for the Muchea South Rd bridge – they range from 24m to 40m in length and weigh between 48 tonnes and 180 tonnes each.
The spokeswoman said work was proceeding on schedule at the NorthLinkWA northern section, with plans for 13 bridges to be completed this year along with 23km of road and a pedestrian-cycle path that will be one of the longest in Western Australia.
The northern section of the Tonkin Hwy extension – from Ellenbrook to Muchea – is due for completion in late 2019.
The 13 bridges to be installed include at interchanges at Neaves and Stock roads and Brand Hwy, a footbridge at Neaves Rd and a pedestrian underpass at Stock West Rd.
Bridge abutments for the project are largely completed, bridge beams are in place at some locations and most bridge deck concrete pours are finished.
Most of the bridges can be built without road detours, but as well as short detours at Muchea South Rd in Bullsbrook and Brand Hw in Muchea a short detour will be necessary at at Cooper Rd in Bullsbrook.
Further information on the works and detours will be provided on the Main Roads travel map and NorthLink WA Facebook page.