We've got one, why haven't you?

That's the message from Melbourne's two northern rivals Sydney and Brisbane concerning an airport rail link.

Tim Anderson, chief executive officer of Sydney's Airport Link rail company said there were many benefits of an airport rail link for Melbourne.

"I support the concept of a Melbourne Airport rail link.  In Sydney, seven million passengers will travel by our airport rail link during 2015.  This reduces road congestion, is good for the environment, and integrates airport passengers into Sydney's entire public transport network. Melbourne would enjoy similar benefits if an airport rail link was established," Mr Anderson said.

The chief executive of Brisbane's Airtrain, Chris Basche, said the airtrain carried almost two million passengers a year.

"In situations such as this weekend when the G20 is on and there are a number of road closures around Brisbane and Brisbane Airport,having an airport rail link becomes enormously critical for the functioning of the city," he said.

He said many other world cities of comparable size to Melbourne already had airport rail links.

"Brisbane has had an airport rail link since 2001 and Sydney has had one since 2000," Mr Basche said.

"Airports tend to value having alternate modes particularly during large events because rail can transport large numbers of people very quickly," he said.

"If you compare a bus with 50 people on it, Airtrain can carry 1000 people a train, so it has a large capacity," he said.

Mr Basche said Airtrain's patronage was growing about 4 per cent a year.

Even Melbourne's Skybus operator is backing a rail link to Melbourne Airport.

 SkyBus director Michael Sewards said with projected patronage numbers increasing annually at Melbourne Airport, by 2030 "the best mass transit solution would require a mix of options including a rail link".

"SkyBus will clearly have a major role to play in this mass transit mix," he said.

"SkyBus' current annual passenger numbers for this financial year are at 3.4 million. SkyBus is currently planning for passenger numbers to increase to 5 million over the next three years and seven million by 2020," Mr Sewards said.

He said in the past four years SkyBus' share of airport visitors had grown from 7 per cent to 10 per cent.

Mr Sewards said Public Transport Victoria and SkyBus were discussing how Myki could be used on SkyBus and in March 2015 Skybus would introduce double decker buses to its airport fleet.

Public Transport Users Association president Tony Morton said a bus would not meet Melbourne Airport's future passenger needs.

"We are looking to a future where public transport carries 50 per cent of airport passengers rather than 10 per cent as it does now," he said.

"If you are looking at change of that magnitude it is not something you can simply do by ramping up the existing Skybus service," he said.

The Coalition has promised an airport rail link if re-elected and Labor said it supports the concept but has nothing planned.

Dr Morton is critical of the timeline for the Coalition's promised airport rail connection. 

"In 2014 talking about something that might happen in 2026 is fairy tales," he said.