The cost of bumper-to-bumper traffic in Melbourne is set to double by 2020, with gridlock sapping $20.4 billion from the national economy by then if action isn't taken.

This bleak assessment is contained in a new government report that paints a picture of increasing traffic congestion and high transport emissions, urban sprawl and surging population growth in the first half of this century.

Melbourne's congestion cost - currently estimated at $3 billion - is projected to be $6.1 billion by 2020, a 103 per cent increase.

The cost is a measure of productivity lost when people are stuck in traffic. The hot spots nationally are Brisbane, Perth and Sydney, with Melbourne coming in fourth.

The report is to be released today by Transport Minister Anthony Albanese and says car dependency in cities is increasing at a rate faster than population growth, creating gridlock and making households hostage to rising oil prices.

It also confirms that Melbourne's population will hit 7 million by 2056.

The report's release could open a new battle front with the states, after the minister signalled that Canberra wants to play a more active role in urban planning and public transport provision.

Mr Albanese is expected to call for a ''collaborative'' approach to deal with future transport policy challenges.

In the report, he emphasises the Commonwealth's inherent interest in cities. Urban policy under John Howard was largely left to the states and local governments.

''In the tradition of Labor governments, the Rudd government has renewed engagement with our nation's cities,'' Mr Albanese says.

''That tradition goes right back to the Whitlam government.

''I believe that cities' policy is core business for the national government - we are, after all, one of the most urbanised nations in the world.''

The report has been compiled by the Major Cities Unit of Infrastructure Australia.

It is not all doom and gloom. The report gives Melburnians a tick for taking practical steps to be clean and green.

Water and electricity use is down, and households have installed ceiling insulation in order to improve their energy efficiency, the report says.

Water restrictions and community awareness prompted 67 per cent of Melbourne households to cut their water usage over the 12 months to 2007-08. Ninety per cent of the population turned off the lights and turned their devices off stand-by, reducing electricity consumption over the same period. The rate of ceiling insulation is higher than in most other capitals. More than 70 per cent of dwellings have pink batts or other insulation.

People in Melbourne are also more inclined than residents of most other Australian cities to leave the car at home and take public transport.

Housing also remains comparatively more affordable in Melbourne. In March 2009, the median house price for established dwellings was $375,000 - a low figure compared with other capitals.

Source: http://www.theage.com.au/national/sitting-in-traffic-to-cost-city-6bn-by-2020-20100304-plv7.html