Melburnians will have to wait at least 15 years before the long-awaited train link to Melbourne Airport and extension of the network to Doncaster and Rowville are rolled out, according to the state's peak public transport authority.

Public Transport Victoria's 20-year vision, released on Wednesday, includes a previously unannounced rail tunnel from Clifton Hill to Fishermans Bend via Parkville and the electrification of railway lines to Geelong, Melton and Wallan.

The 20-year plan is currently uncosted, featuring only one dollar sign in its 140 pages. Credit:Jason South

It is meant to create the capacity to carry a forecast 1.7 million passengers a day by 2031. But the plan is uncosted, features no new projects and contains just one dollar sign in its 140 pages. When pressed on a price estimate, PTV chief executive Ian Dobbs said: ''If you want a rough number it's probably about $30 billion.''

The development plan, dated December 2012, is broken down into four stages over 20 years. The project calls for upgrades to the city's signalling system to improve traffic flows, as well as duplication of railways and electrification of others.