More than 50 of Melbourne's busiest road intersections will be removed by replacing traffic lights and roundabouts with underpasses if the Coalition wins government next year.

Opposition Leader Matthew Guy has pledged "the biggest traffic congestion-busting project in Victoria's history" and will spend billions of dollars grade-separating major intersections around Melbourne and Geelong.

The project is modelled on Labor's popular level crossing removal program, but is targeted solely at roads.

"Census data shows that 74 per cent of Melburnians take a car to work every day," Mr Guy said. "That's why more of the same band-aid approach to addressing traffic congestion won't work."