A long-awaited rail link to Australia's second busiest airport isn't "an unworthy project" but Victoria's premier is in no rush to build it.

Melbourne Airport is concerned Infrastructure Victoria’s (IV) draft strategy envisions the airport rail link – expected to cost up to $5 billion – being built between 2030 and 2045.

The airport points to its own passenger forecasts that suggest the Tullamarine Freeway will hit capacity during peak hour in the late 2020s.

“It is essential that a rail link to Melbourne Airport is delivered within the next 15 years,” the airport’s submission to IV states.

Premier Daniel Andrews says the public transport system must be improved methodically, beginning with level crossing removals, increasing capacity on the rail network and building more trains.

“That doesn’t mean an airport rail link won’t happen at some point in the future but the order in which you get it done is the really important thing,” Mr Andrews told reporters on Tuesday.

“It’s not an unworthy project – let’s be clear about this.”

Melbourne Airport says a rail link would “extend well beyond” the easing of congestion on the surrounding road network and suggests a comprehensive planning study should begin next year.

It agrees with IV’s assessment that priority access should be given to the bus service that runs express from the city to the airport.

But it cautioned a SkyBus-only solution might entice airport workers to commute via the city – which could worsen Melbourne-wide congestion.

Melbourne’s airport moved 33.7 million passengers in 2015/16, making it the nation’s busiest airport outside Sydney.

IV is expected to deliver its final report on Victoria’s short, medium and long-term infrastructure needs and priorities within weeks.