The accompanying chart shows how public transport’s share of the journey to work varies with population density across 41 US and Australian cities.
It is taken from the same article that I mentioned in my last post. The authors, Dr John Stone and Dr Paul Mees, find there is only a modest relationship between population density and transit share (R2 = 0.229). They conclude that “higher density across the whole urban region is not the explanatory variable that many might expect”.
Los Angeles, for example, is the densest metropolitan area in the US – denser ever than New York – yet the chart shows public transport’s share of work travel in LA is much smaller than in NY.
If that seems counter-intuitive, your intuition could be right. The chart uses average population density calculated across the entire urbanised area of each city.
While that’s perfectly alright in some contexts, it doesn’t allow for the possibility that public transport’s ability to win travel away from cars is related to the morphology of density – the ‘peaks and troughs’ in the way the population is spatially distributed. It’s possible that the relative proportion of population in high density areas vs low density areas has a greater impact on mode share.
Using average density probably won’t present a serious problem with cities like Atlanta, Austin, Dallas, Phoenix and Portland where the population is overwhelmingly suburbanised at relatively uniform (low) densities. But it could have a big impact on places like New York which have an extensive ring of low density suburbs as well as a high density central region e.g. Manhattan and Brooklyn.
A way of dealing with this issue is to use weighted density rather than average density. This involves weighting the density of each suburb (or other convenient geographical unit e.g. traffic zone) by its share of the city’s total population. So a one km2 suburb with 5,000 residents (say) carries a lot more weight than another suburb of the same area that has only 1,000 residents. Read the rest of this entry »
According to a report in The Age last month, new research published in the latest issue of Australian Planner shows that higher suburban densities are not a precondition for vastly better public transport. Reporter Andrew West says:
City dwellers have been presented with a false choice – live in apartments and enjoy good public transport or retain the house and land and rely on cars
The research by Dr John Stone and Dr Paul Mees contends that it is not necessary to intensify land-use across the whole city before significant improvement in both patronage and economic efficiency of public transport becomes possible.
They say the contribution made by urban consolidation “to recent public transport patronage growth is modest and makes little impact on the density of the whole urban region”. Most residents of Australian cities will continue to live in houses and suburban subdivisions that are already built so “alternatives to the car will need to be effective at existing urban residential densities”.
They argue instead for a ‘networked’ model of public transport. Improving the way existing public transport resources are managed – especially by providing higher frequencies and improving coordination between services and between modes – will yield significantly higher transit patronage in the suburbs without the need for broadbrush increases in density.
I’ve argued before that increasing residential density, by itself, will not necessarily increase public transport patronage significantly, much less shift travellers out of their cars in large numbers.
I’ve also argued that there are generally better gains to be had from using existing resources more efficiently rather than relying on strategies based around huge new infrastructure investments or massive land use changes.
And I think the idea of networking public transport is absolutely critical. By embracing transfers, networking provides faster travel paths to all parts of the metropolitan area than is possible by radial routing.
However it’s not obvious to me that ‘networked’ public transport, by itself, would have the sort of major impact on mode share in the suburbs implied by The Age’s report. I can see that it would make public transport much better for existing users and I’ve no doubt it would increase patronage, but I’m not persuaded that it would be enough to address the ‘false choice’ that The Age says Melburnites have been presented with. Read the rest of this entry »