Twelve years have passed since the Carr government's "Action for Transport 2010" blueprint promised a slew of new public transport and motorway infrastructure. While only a fraction of the promised rail and bus projects were delivered, all the roads were, plus others that were not in the plan.

But the Roads and Traffic Authority is pushing to duplicate the M5 motorway at a cost of $4.5 billion, which would prohibit the simultaneous construction of other significant transport infrastructure. If the RTA plan goes ahead we can kiss goodbye to the north-west and Parramatta-Epping rail links for at least a decade.

Sydney needs a better approach. Why even consider widening the M5 and building another massively expensive four-lane road tunnel, when an alternative package of public transport projects and policies can slash traffic congestion on the M5 and elsewhere, improve freight-handling efficiency and provide new cross-regional links between the western and south-western suburbs and the jobs in eastern Sydney, and do it for less than a third of the cost?

The key question is: where do all those peak-period cars on the M5 come from? Where are these people going?

We know they're not going to the central business district. Because of its excellent public transport access, very few of the CBD's 230,000 workers drive. Three-quarters arrive by public transport, most by rail.