New York has a great public transport system but it doesn't prevent traffic congestion or the use of roads for parking (source: Nadine Mansfield)

ABC News reported yesterday that the CEO of Victoria’s roads authority, John Merritt, says Melbourne will need more than new roads to deal with growing traffic congestion; motorists will also need to shift to public transport, walking or cycling and live closer to where they work.

We can’t just build our way out of congestion. We need to invest heavily in public transport, which we are, through Melbourne Metro and we need to encourage people to cycle or to walk and make that feel as safe and as practical as we can.

There are significant, large projects but there is no one big answer to this, it is a series of pieces of work. Then there are those changes in behaviour – getting people to use public transport and encouraging more people to ride.

He’s right of course; building more roads in Australia’s increasingly dense cities won’t reduce peak hour congestion; induced traffic will fill up any new road capacity sooner rather than later.

You’ve only got to look at cities like Los Angeles to see that freeways don’t make a serious dent in traffic congestion.

But building more public transport won’t reduce congestion either. The road space vacated by motorists who shift to a new or upgraded train service will soon be taken up by other motorists i.e. by induced traffic.

You’ve only got to look at places like London and New York to see that even having a very high standard of rail-based public transport does not reduce – let alone eliminate –  congestion.

Something needs to be done about traffic congestion of course but the solution doesn’t lie in providing more infrastructure. Even putting aside the issue of induced demand, the financial and social cost of retro-fitting enough new road and rail capacity in urban areas to have measurable impact on traffic congestion would be astronomical.

The only plausible way to reduce congestion in established areas is to ration access to road space. That could be done administratively, for example based on number plates, or more efficiently by putting a price on using roads in peak periods i.e. by introducing congestion charging (e.g. see Are motorways the only answer to traffic congestion?).

That doesn’t mean there aren’t other reasons to build new infrastructure. A key benefit new projects provide is an increase in the total number of travelers who can get to destinations in peak periods even if, as is ultimately inevitable with new roads, it brings no reduction in traveling time.

What’s really needed though is a broader view of what to do about cities that goes beyond the focus on traffic congestion and thinks more in terms of how to improve accessibility, livability and affordability.

I’ve made the point before (see Are politicians doing what’s necessary to grow our cities?) that building infrastructure is only one  of a number of steps necessary to prepare Australia’s major cities for future growth.

Governments need to commit to structural changes like sweating existing assets much harder, suppressing and/or shifting the demand for travel at peak periods, aligning taxes and charges with the real social cost of activities like travel, and lowering the cost of building and operating transport infrastructure.

They also need to reduce regulatory constraints on higher density development, make housing markets more flexible, develop a much better understanding of likely future changes in transport demand and technology, and pick infrastructure projects with more regard for their social value than their political utility.

Such a program of action will be politically difficult but that’s inevitable if we want better cities.