Melburnians have been talking about a train to Tullamarine Airport since well before it opened. Now Prime Minister Malcolm Turnbull has made clear his enthusiasm for an airport rail line, with or without state government support.

But these conversations need to move beyond the question of getting travellers between their plane and their city hotel.

Beyond airport access, this proposal highlights the potential for rail projects to shape Melbourne and feed an integrated public transport system that could serve its growing population.