The Transport Minister Troy Buswell has marked the beginning of works on the Mitchell Freeway and Northbridge tunnel widenings.
The $57 million project involves adding an extra lane on the freeway northbound to Hutton Street.
An extra tunnel lane will open in May.
Mr Buswell says while there will be some disruption to motorists, he is confident the roadworks will not hurt the Government at next month's state election.
"Anybody who travels north from Perth around Lake Monger in the afternoons understands that that road network isn't coping," he said.
"I think the minor inconvenience of the widening works will be more than offset by the fact that people will at long last know that a solution is being put in place."