THANKS to lack of public transport, at least 50 per cent of homes in Baulkham Hills and the Hawkesbury are among the 635,000 households in NSW with more than two cars, boosting the extra million cars on Sydney's roads since 1996.

Thousands of drivers from the north-west pay $21.14 a day in tolls for the return 70-kilometre journey to the city and now several academics propose a 10-15 cents a kilometre congestion tax on road users to cut Sydney's ever-worsening traffic.

With the number of car trips in the morning peak expected to climb 83,000 to 250,000 within five years, Peter Stopher and Camden FitzGerald, from Sydney University's Institute of Transport and Logistics Studies, say the proposed tax could dramatically ease congestion.

The authors' report, published in The Sydney Morning Herald, said so many cars clogged the city that it would require the equivalent of about 14 Lane Cove tunnels a year to accommodate the increase.

A similar congestion tax in London had helped cut unnecessary car trips to the city centre and modelling by the institute's director, Professor David Hensher, indicated a similar scheme would cut Sydney's congested traffic by up to 8 per cent during peak periods.

A poll of 1609 Herald readers has enthusiastically supported the congestion tax proposal, with 37 per cent of respondents in favour, 32 per cent in favour ``up to a point'', and 28 per cent saying ``no''.

But the federal MP for Mitchell, Alex Hawke, joined the NSW Roads Minister Eric Roozendaal and Hills News readers (vox pop, page 12) in slamming the report.

Speaking in Federal Parliament, Mr Hawke raised the matter of excessive tolls for Mitchell motorists and condemned the State Labor Government for its practice of closing public roads to force people into tollways.

``I find it particularly ironic that the day after I raised this matter of great concern to motorists in north-west Sydney we have an out-of- touch academic calling for another charge to be levied on already suffering motorists - a proposal which rather than calling for greater investment in public transport or alternative solutions seeks to further slug motorists in the most infrastructure deprived region of Australia.''

``With the highest rate of car ownership in the country, residents in Mitchell do not have a choice in driving as there are very few, if any transport alternatives servicing north-west Sydney. This is in the face of already existing tolls, levies, taxes and infrastructure charges on properties.''

Mr Hawkes said a more practical measure would be a levy on all academics who come up with impractical and ill thought out proposals that have no application in the real world.

``With the amount of impractical suggestions that are proposed each year by academics, this type of levy would raise a significant amount of money to help fund infrastructure,'' he said.