Victorian leader Ben Carroll on Sunday announced the Western Freeway would get additional lanes and lights, and improved interchanges, if Labor won the November poll.
The $550 million boost adds to a previous, $1.1 billion federal Labor funding pledge.
"Members of Melbourne's western suburbs community have been calling for years to have the Western Freeway upgraded," Mr Carroll told reporters.
The recently sworn-in premier added he believed voters wanted a relentless focus on Victoria's basics.
"There was nothing more important than getting our road infrastructure right, making sure hardworking Victorians can spend less time in traffic and get to spend more time with their families," he said.
"I've made it a big priority of mine - roads ... Business as usual is not good enough."
Interchanges at Ferris, Leakes and Hopkins roads are earmarked for upgrades.
The Royal Automobile Club of Victoria previously rated the Hopkins Road intersection western Melbourne's most dangerous.
Thirty kilometres of additional lanes will be complemented by a consistent 100km speed limit between Ferris Road and Ballarat Road.
Roads Minister Paul Hamer promised the upgrades would mean safer, quicker and more reliable journeys for all western suburbs residents.
Federal Labor MP Sam Rae welcomed the state commitment as estimates pointed to climbing demand for the motorway.
"There are 86,000 cars a day using this," he said.
"This is, of course, the fastest growing part of Australia, and before long, that'll be well over 100,000, and up to 113,000 in the short term. So this is investment that's so dearly needed."
In April, the federal Infrastructure Department revealed funding flows were stalled as it was still waiting on state government planning work.
The Victorian government submitted key information and a $50 million allocation for the freeway was unlocked in May.
The latest pledge will make further funding available.
Both Labor and the coalition have announced major infrastructure plans ahead of the November state election.
Liberal leader Jess Wilson announced a $288 million rural road spend, spanning the state's 48 regional councils.
The opposition on Sunday also unveiled an election commitment targeting medical workers.
Doctors, nurses and other health professionals would receive incentives of up to $10,000 in the state's regions under a coalition government, Ms Wilson said.
Tree-changers could receive both an up-front transfer and ongoing, yearly stipend for staying in rural jobs.
The opposition did not detail how the cash would be delivered, but indicated it would be modelled on similar rural workforce initiatives in NSW.
An August DemosAU/PremierNational poll gave the coalition an election-winning lead over Labor, but strong support for One Nation made the result difficult to predict.
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