Roads that are to be upgraded in Melbourne's west will be at their capacity by the time works are completed, Opposition Leader Matthew Guy says.
The Victorian government is promising to spend $1.8 billion fixing and maintaining 700 kilometres of roads stretching from Werribee to Footscray.
From 2018, eight high-priority roads will be upgraded over five years, while maintenance will continue for 20 years.
"The reality is by the time they're completed the roads will still be clogged," Mr Guy told reporters on Tuesday.
He added "uncontrolled population growth in the west" would add to traffic over the years.
Premier Daniel Andrews says the project will cut congestion in the area.
"This is one of the biggest ever projects to update suburban arterial roads and it's going to create jobs, cut travel times and congestion and improve safety," he said in a statement.
Lanes will be duplicated or widened to boost capacity and road pavements will be improved with intersection upgrades.