Premier Daniel Andrews and Transport Infrastructure Minister Jacinta Allan on Thursday announced the agreement with Spark consortium to deliver the main works involved in the $15.8 billion toll road.

The project, jointly funded by state and federal government, will connect the M80 Ring Road to an upgraded Eastern Freeway.

It is tipped to cut travel times between Melbourne's north and southeast up to 35 minutes and take 15,000 trucks off local roads each day when completed in 2028.

As part of the deal, a series of changes have been made to the original design, the most significant being the extension of the tunnels by 1.9 kilometres.

Toll money collected will go to the state government as part of the deal with Spark.

Ms Allan said the design of the tunnel was a "significant improvement" from the initial plans and will reduce disruption during construction and create more room for parklands and wetlands, including a 10-hectare community park.

"It is fair to say this is an additional investment," Ms Allan told reporters in Bulleen.

"When we're presented with opportunities to improve projects and improve community outcomes ... We take those opportunities."

The new design will also pave the way for Greensborough Rd to be transformed into a tree-lined boulevard, forming a "green gateway" to Watsonia with new multi-level train station parking and new community spaces.

"Something like 50 MCGs worth of open space is going to be created and supported through this design," she said.

No additional homes are expected to be acquired under the design changes.

A voluntary purchase scheme is available for 36 affected homes and some businesses.

Ms Allan said the project had been talked about for more than 60 years and would provide more opportunities for workers to travel to and from economic hubs on opposite sites of the city.

The premier described it as "one of the very biggest road projects anywhere in our country".

The Spark consortium comprises WeBuild, GS Engineering and Construction, CPB Contractors, China Construction Oceania, Ventia, Capella Capital, John Laing, DIF and Pacific Partnerships.

Australian Associated Press