But an analysis for the Herald by one of Australia's leading motorway experts, Dr Michelle Zeibots, finds the upgrade would also require a vast and expensive network of feeder roads cutting through residential neighbourhoods. And such a network - of at least five mega-roads - is under consideration.

The Government's own 2031 Transport Blueprint, which is now under review, includes plans for an M4 East between Strathfield and Rozelle, a link between the M4 and Port Botany, and a link from the M2 at Lane Cove to the F3 at Wahroonga.

The blueprint reflects a report from the consultancy Evans & Peck, which urges $23 billion worth of road-building: it includes the F6 through the St George region and Sutherland Shire; the M4 East, an inner-west bypass from Port Botany to Rozelle; a motorway linking the M4 East to the M2 in Lane Cove, and the M2-F3 tunnel.

The Transport Minister, David Campbell, said: ''The Transport Blueprint is being finalised and that will set out the Government's transport plans over the next 25 years for NSW.''

Paul Forward, who is associated with Evans & Peck, also chaired the Blueprint reference panel for the Government.

Dr Zeibots, a researcher at the Institute for Sustainable Futures at the University of Technology, Sydney, said the projects would ultimately benefit no one.

''The Government's plan to duplicate the M5 East is meant to relieve congestion, but you then need to build parts of the F6 to divert traffic away from a bottleneck at General Holmes Drive,'' she said.

''This would generate a new bottleneck at St Peters, needing more road construction that would generate even more traffic, creating a vicious cycle of expensive projects that benefit no one. Motorways beget more motorways and congestion never goes away.''

Analysing data from the NSW Roads and Traffic Authority and the NSW State Plan, Dr Zeibots found annual average daily traffic volumes in the General Holmes Drive tunnel, which links the M5 East and the Eastern Distributor, rose from just over 87,000 to 133,000 immediately after the M5 East opened in 2001. It reached its capacity of 140,000 in 2005, where it sits today.

Across the city, the average speed in the morning peak hour on seven major roads - including all but one of Sydney's motorways - has also fallen, from 34 kilometres per hour in 2003 to 30 kilometres per hour in 2008. ''Quite clearly, motorway building has not reduced congestion otherwise speeds would have improved,'' said Dr Zeibots. ''Instead, they've fallen.''

If the Evans & Peck master- plan and the blueprint were implemented, the result would be widespread disruption across Sydney. The F6, from St Peters in the north to Loftus in the south, would cut into Brighton-le-Sands, Ramsgate, Sylvania Waters, Miranda and Gymea, and also slice through the north-western corner of the Royal National Park.

The ''Inner West Bypass'', based roughly on the route of the abandoned Johnston's Creek Extension Road, would run from St Peters underneath Enmore, Stanmore and Camperdown to Annandale, where it would join the City West link. Although it would be a tunnel with a $12 billion price tag, it would require four to five ventilation stacks that would concentrate plumes of car exhaust in the surrounding neighbourhoods.

The Evans & Peck proposal links the Inner West Bypass directly to a new tunnel that would follow the Victoria Road alignment from Rozelle to Hunters Hill and then to Lane Cove, where it would join the M2. A new tunnel would follow the Pacific Highway alignment from Pymble to Wahroonga, where the F3 begins.

PDF of Proposed Motorways map - www.smh.com.au/pdf/roadsweb.pdf

Also see - Slow trains push commuters onto motorways

Source: http://smh.drive.com.au/labyrinth-threatens-to-eat-city-20100115-mcgg.html