Transport arteries define how efficiently goods and people move in major cities.
Rail was critical to the growth of great cities like Melbourne, but fixed tracks can only offer service for hub and spoke travel patterns.
Roads offer greater transport flexibility and now play the key role in cities as job and income providers.
Melbourne is one of a few world cities where public transport's share of journey-to-work travel to the central business district has increased in recent years.
Public transport now accounts for half of CBD work trips, but for all Melbourne's travel public transport accounts for only 15 per cent of work trips and even less for total trips.
Fixed rail systems cannot service the increased diversity of trip destinations and origins.
Even handling increases in demand on existing routes will require major new capital investment.
This aggravates government transport problems. Not only are trains intrinsically and increasingly less able to service demand, but passengers refuse to pay the full costs of public transport.
Typically, passengers pay less than one third of Melbourne's rail and tram system budgets, and about 40 per cent for bus travel.
As public transport users form powerful lobbies to prevent price rises, governments are reluctant to spend money.
By contrast, road vehicles pay their way in specific taxes and through tolls.
In the 1980s under the Cain/Kirner ALP government, unions in Victoria dictated transport planning. Unions were hostile to new motorways, which they saw as competition to rail and tram workers' jobs.
Union pressures were augmented by a growing strength of environmental protesters against the Eastern Freeway.
Government policy responded. ''No new freeways'' became the catchcry.
Arterials roads built were underfunded and often congested, prompting the South Eastern to be commonly referred to as the ''car park''.
This changed during the 1990s, under the Kennett government, which pushed modern roads including the Tullamarine and M80.
Green groups have, however, become increasingly powerful in opposing infrastructure developments.
The Bracks/Brumby ALP governments 1999-2010 became progressively more vulnerable to these pressures and we saw decreased road spending and increased congestion.
Eventually, the Brumby government tasked Sir Rod Eddington to advise on future development.
The Eddington report proposed, at a cost of $9 billion apiece, the completion of the Eastern Freeway and an underground rail link.
In addition, new bus services and new bicycle tracks were offered to placate the opponents of cars and trucks.
Premier Brumby grasped the plan.
He recognised that road development is essentially motorist-funded and increased journey times threatened Melbourne's efficiency, while major rail spending could be deferred.
But Labor lost office.
The Coalition's initial priority was on reining in budget blowouts.
Road planning was largely confined to ridiculous ''flora and fauna'' reports for an east-west link that cuts through the centre of the city!
Now roads are back on the agenda, but the ALP in Opposition, mindful of Green rivals, has reneged on its former support for completing the Eastern Freeway.
For its part, the Government has declined to publish the costs, possibly because they have blown out from the previous $9 billion tag.
Melbourne needs road upgrades but will face noisy political fights with every proposal.