The $300 million Mordialloc Bypass will be built as a freeway, with the Andrews government today committing an extra $75 million to grade separate three intersections along the planned route.

The four-lane Mordialloc Freeway will connect the Frankston freeway to the Dingley Bypass, with interchanges at Springvale Road, Governor Road, Lower Dandenong Road and Centre Dandenong Road.

It's due to open in 2021, with Premier Daniel Andrews promising to keep the new arterial toll-free.

Mr Andrews has promised to keep the new arterial toll-free. (VicRoads) (Supplied)

Mordialloc MP Tim Richardson said the decision to change the project's scope followed extensive community feedback.

"We've listened to locals who've told us they want this road as a four-lane freeway, and we're getting it done,” he told 9NEWS.

Roads Minister Luke Donnellan said the government expected the freeway to deliver significant travel time savings.

"By building the Mordialloc Freeway we're giving drivers a continuous trip from Frankston to Clayton with no traffic lights, and taking ten minutes off the trip", he said.