New lanes have opened on the Monash Freeway and the speed limit has been raised. Credit:Joe Armao

The speed limit has returned to 100 km/h on the Monash Freeway, with motorists saving more than seven minutes on a trip along the length of Melbourne's busiest road.

But as the new freeway lanes between EastLink and Clyde Road were declared opened on Sunday, an even bigger expansion of the Monash Freeway is being planned from next year.

Victoria's Acting Premier James Merlino said the first stage of the Monash Freeway upgrade had been completed, at a cost of more than $1 billion.

The cost has been shared between the state and federal governments.