The Transport Department and its successor, Public Transport Victoria, were never interested in the Coalition's vision of new suburban rail extensions because they had already looked at these projects years ago and found reasons not to go ahead with them. Evidently they won the argument behind closed doors, because the government has rushed to release its reports, as if to purge itself of the embarrassing baggage of its pre-election optimism.

Released on Thursday, the Doncaster rail draft report appears so expensively elaborate it is as if it were designed to fail.

A brand-new tunnel would be required not just for the Doncaster line but also from Northcote into the city along the South Morang line, where it would join Melbourne Metro in Parkville before terminating at Flagstaff. Passengers would hope that station is open on weekends by then.

The Melbourne Airport rail link would also connect to Melbourne Metro and run alongside the Sunbury line before detouring to Tullamarine at Albion East. At 30 minutes, it would be a slower run to the airport than the average ride on Skybus.

A Rowville line has also been judged unfeasible without Melbourne Metro because of congestion in the City Loop. Voices outside government argue a new rail tunnel is not the only answer to Melbourne's rail capacity woes. High-speed signalling, for example, could double capacity at much less cost.