The number of passengers passing through Melbourne Airport will double to 70 million a year over the next two decades, according to the airport's boss, who says plans for rail and road infrastructure must be put in place now to handle such growth.

Melbourne Airport chief executive officer Lyell Strambi said the expansion of the Tullamarine Freeway was welcome but could return to gridlock in as few as 10 years.

Passenger numbers will hit 70 million a year by 2037, Melbourne Airport says. Credit:Paul Rovere

"That's exactly why we're out there saying we need the next solution – we really do need the government to be delivering on the rail project," he said.

"Given that's got a 10-year lead time, now is the right time to start."