Should the war on obesity be a key objective of transport policy?

I know people who have the option of driving but instead take the train so they can improve their physical fitness. It takes longer than driving, but since they’re going to work anyway, walking to the station is an easy way to exercise. It makes good sense; I’ve walked or cycled to work at various times for the same reason.

However it’s one thing to make a private choice to use public transport in order to exercise – it’s another thing altogether to elevate the war on obesity and other health issues, as a matter of public policy, to the status of a key goal of the transport system. That’s what organisations like the Planning Institute and the National Transport Commission propose, but it’s not self-evident to me that it’s a good idea. It’s worth thinking about it further.

There’s a paradox here. The very point of public transport is to extend personal mobility. At the end of the nineteenth century when everyone other than the very wealthy walked, the arrival of trams and trains greatly enriched people’s lives by overcoming the limitations of walking. Now they could travel further to better jobs or better houses, take the family to the beach on Sunday, or visit friends and relatives in more distant suburbs. The whole point of public transport was to travel faster than walking so people could travel further in the same time.

The panoply of exercise-related issues like obesity are not a transport problem, they’re a social problem. They’re a result of eating more and of expending less effort in all aspects of life, not just in the way we travel. It’s true we are much more likely today to drive than walk, cycle or use public transport, but the avoidance of effort is true of almost everything we do.

Most of us work in jobs that don’t involve anything even remotely like the level of physical effort expended by the average worker of a few generations ago. If we did, Occ Health and Safety would have a fit. On the home front, we’ve had “labour saving” devices like refrigerators, stoves, washing machines and vacuum cleaners for generations. Television and home delivered newspapers mean we don’t even need to go out to get information and entertainment.

Consider the giant strides we’ve made in avoiding exertion over the last twenty years. Computers have eliminated the effort of going to the bank, the booking office, the travel agent or the bookshop. We blow leaves rather than rake them, we use power tools to drive nails and screws, we answer the phone without getting out of our seat, and we cook meals without having to prepare them. We control our air conditioners, central heating, TVs and sound systems with remotes. Climate control means our bodies don’t even consume much energy to keep warm – many children barely know what it means to shiver.

The decline of effort pervades all aspects of our lives, not just how we travel. For better or worse, it’s one of the ways we define progress. So transport – and that essentially means the car – is only one part of the health problem.

And in fact it’s a relatively small part, because the main cause of obesity is what we eat, not how little we exercise. It’s likely to be far more effective to target food than public transport.

Lennert Veerman, Senior Research Fellow at Queensland University’s School of Population Health, points to a recent study which argues the main force driving the obesity pandemic is an increase in consumption. He says the 1970s was:

When the food supply started to change radically. The supply of refined carbohydrates and fat increased and more food was mass prepared rather than cooked at home. The era of easily available, cheap, tasty, highly promoted, energy-dense foods had begun. This view of the causes of the rise in obesity prevalence suggests the likely solutions lie in the area of the supply and promotion of food. And research supports that notion.

He says if governments are serious about tackling obesity their priority should be food. They should tax unhealthy food, limit advertising and restrict availability in schools. He also says healthy food should be subsidised. Read the rest of this entry »


Is inner city living the solution to obesity?

How much exercise is needed to burn off food?

It’s often pointed out that residents of the inner city, on average, are less obese than residents of the outer suburbs. Since the inner city is denser, more walkable and has much better public transport access than any other part of the metropolitan area, the conclusion seems obvious to many – a key strategy to address obesity should be to encourage higher dwelling densities and better public transport in the suburbs, especially the newer, fringe areas.

The flaw in this thinking is it fails to observe that the inner city – defined roughly as the area within 5 km of the CBD – is a different world. Relative to the suburbs, the inner city has an emphatic over-representation of younger, well educated and affluent residents with fewer dependents. The proportion of the population made up of young singles is three times that of the metropolitan area as a whole and there are twice as many young couples without children.

These are the sorts of people who on average are slimmer because they’re younger, who are of an age where appearance is enormously important, and who are well educated enough to know about nutrition and eschew fast food. They can afford to buy high quality fruit and vegetables and pay for gym memberships. Because they’re more affluent, they have fewer children on average and hence less need for a car.

They live in smaller dwellings so they can be near the CBD and take advantage of its enormous and unparalleled concentration of high-paying professional jobs, its matchless endowment of cultural attractions and its huge and diverse range of social and entertainment opportunities. There’s no other concentration of activity within the metropolitan area that comes even close to the richness of what the inner city offers.

Because they live at higher density, driving is too hard for many trips – roads are congested and parking costs range from expensive to impossible. So residents often walk or use public transport instead. That’s O.K., because they happen to live in that transit-rich, small and unique geographical area where every train line and tram line in the entire metropolitan area – the result of 130 years of construction and at least one spectacular land boom – converges.

So population density and access to public transport are not the underlying forces driving this group’s superior average BMI. Rather, it’s a combination of the small but highly specialised group who can afford to live there, on the one hand, and the special characteristics of the area, particularly the presence of the CBD, on the other.

It’s pie in the sky to imagine the sheer scale and complexity of the highly specialised attributes offered by the inner city could be replicated in the suburbs – much less the outer suburbs – within the foreseeable future. The inner city is focussed on the CBD and in almost every city in the world, the number of jobs in the city centre is an order of magnitude larger than any suburban centre (Atlanta is possibly the sole exception). In Australia, the centre offers the cream of corporate jobs.

The importance of proximity to the CBD in explaining the special character of the inner city is demonstrated by the fact walking’s share of work trips plummets from 13% in the inner city to just 2% immediately one locates in the adjacent inner suburbs. This share is only marginally better than the outer suburbs.

Will building at higher densities and providing better public transport in the outer suburbs significantly lower the incidence of obesity? Not likely. Even if all outer suburban dwellings were townhouses, the incentive to walk is much lower if there’s no CBD, cultural precinct, river, beach, historic buildings, hundreds of cafes, and hundreds of thousands of jobs to walk to. Perhaps most importantly, the outer suburbs don’t have the constraints on driving and parking that often make walking or public transport a superior alternative in the inner city. Read the rest of this entry »


Is it healthy to assume correlation means causation?

Association of obesity trend in the US with vehicles miles travelled (left) and with Justin Wolfer's age (right)

The link between the physical environment and health outcomes like obesity is fraught. The Victorian Legislative Council’s Environment and Planning References Committee should bear this in mind as it goes about its new inquiry into the contribution of environmental design to public health.

The Committee might want to start with the first chart in the accompanying exhibit, which comes from a recent issue of The Economist and purports to show that obesity has increased in the US in line with the increase in miles driven over the last 15 years. The chart is based on work done by researchers at the University of Illinois who found “a striking correlation between these two variables – but with a large time lag……This near-perfect correlation (99.6%) permits predictions about obesity rates”.

Expatriate Australian economist and Wharton business school Assoc Professor, Justin Wolfers, points out the folly of this claim. It is, in his words, a “nonsensical correlation”:

When you see a variable that follows a simple trend, almost any other trending variable will fit it: miles driven, my age, the Canadian population, total deaths, food prices, cumulative rainfall, whatever.

To demonstrate his point, Professor Wolfers prepared the second chart showing an even better correlation between changes in obesity over the period and changes in his age – he didn’t even need to resort to a time lag to get such a good fit! He acknowledges The Economist offered the customary caveat that correlation does not equal causation but this chart, he says, is so completely unconvincing as to warrant a different warning: “Not persuasive enough that you should bother reading this article” (in the interests of balance, here’s The Economist’s subsequent response to Professor Wolfer’s charge).

This exchange highlights a problem with much of the research that purports to show the physical environment — particularly density and/or public transport access —  has a strong effect on health-related variables like obesity. There’s plenty of evidence of correlation but not much evidence of causation. There’s no doubt obesity is inversely related to both density and access to public transport, but if it turns out these aren’t the underlying drivers of obesity then the economic cost of misdirected policies could potentially be significant.

There are special reasons why it’s hard to establish causation when dealing with real life infrastructure projects and transport/land use programs. These British epidemiologists reviewed 77 international studies examining the effectiveness of policy interventions to reduce car use. They concluded the evidence base is weak, finding only 12 were methodologically strong – and they mainly involved relatively small-scale initiatives like providing better information about travel options or direct financial incentives to reduce driving (incidentally, only half of those 12 actually worked i.e. reduced car use). Read the rest of this entry »


-Are there really limits to what planning can do?

States' and Territories responses to 23 land use planning 'challenges'

There are, but in Victoria those limits appear to be very elastic.

Because it controls the use of land, the whole complex edifice of planning regulation touches to a greater or lesser extent a lot of the things we do.

In a newly released report commissioned by COAG, the Productivity Commission gives us an insight into how the nation’s planning agencies think the land use control system influences our lives.

The report, Performance Benchmarking of Australian Business Regulation: Planning, Zoning and Development Assessments, examines the regulatory frameworks of each jurisdiction, the processes for supply of land, the bases for assessing developer contributions, compliance costs for business, and competition issues arising from planning decision-making.

As part of its investigations, the Commission asked each State and Territory to answer this question: “To what extent can government use the planning, zoning and DA system to positively influence the following challenges”?

The answers each jurisdiction provided to 23 “challenges”, graded from “no effect” through to “major effect”, are shown in the accompanying chart (copied from the report). The survey was completed between October and November 2010, prior to the Victorian State election.

Bear in mind that the survey relates specifically to the powers of land use planning agencies i.e. not transport or other agencies. Also, the planners were specifically asked about the scope to positively influence each of the challenges. There are some interesting claims here and some equally interesting comparisons between States and Territories.

There’s a consensus that, given (presumably) the right policies, land use planning can have a major positive influence on managing greenfield development, accommodating population growth, managing the transition to higher population densities, providing diverse/appropriate housing, and protecting biodiversity.

By and large I’d agree with that. My only caveat would be the understanding that some of the benefits will come from reducing rather than increasing the degree of planning intervention. A prime example is the many restrictions on constructing higher density housing within established urban areas.

Where the survey gets really interesting is outside these five key areas. Victoria in particular stands out from its peers. Read the rest of this entry »


Do more fast food restaurants make the locals fat?

Distribution of BMI for people living in US towns adjacent and non adjacent to interstate highways (note there are 2 curves)

It’s commonly taken for granted that a disproportionately large number of fast food stores in an area is a key reason why the local population often has high rates of obesity.

The California Centre for Public Health Advocacy, for example, argues that “there is growing scientific evidence that what people eat—and their likelihood of being obese—is influenced by the food environment in which they live”.

More people are going to fast food restaurants where the food is high in calories and portions are large. Many respectable studies have shown a clear correlation between average body weight and eating out. According to one, growth in the number of restaurants accounts for as much as 65% of the rise in the percentage of Americans who are obese.

Various policies have been proposed to break the evident connection between fast food restaurants and obesity. These include proposals to limit the number of fast-food restaurants, ‘fat taxes’, limits on fast food advertising and mandatory calorie counts on menus.

But do fast food restaurants really cause obesity? As with many things, appearances may be deceiving. Correlation doesn’t mean causation.

This study, Are Restaurants Really Supersizing America?, by UC Berkeley researchers Michael Anderson and David Matsa, poses this question: “do more restaurants cause obesity or do preferences for greater food consumption lead to an increase in restaurant density?”.  Read the rest of this entry »


Can public transport “solve” the obesity epidemic?

My entry in Ted Baillieu's (proposed) competition. Flinders St Station - originally planned Swanston St elevation

A new US study has found that there is a significant association between public transport use and reductions in Body Mass Index over time.

This study has excited a lot of attention because it used a before-and-after “natural experiment” (see here, here, and here).

The researchers did an initial “before” telephone survey of residents living within one mile of a proposed new light rail line in Charlotte NC. They followed up with an “after” telephone survey 6-8 months after the new line opened.

There are some major methodological limitations with the study. Respondents self-reported their weight. The initial sample of 839 fell to 498 respondents in the follow-up phase. Only 26 respondents used the new line to commute on a daily basis.

Nevertheless, I have no difficulty with the proposition that those who choose to commute by transit are likely to be thinner than those who choose to drive to work. After all, transit requires the expenditure of more calories on walking and standing than driving does.

But in my view, the key issue is to what extent better health outcomes – and in this context specifically weight reduction – should shape transport policy. In order to look at that issue it is essential to understand what’s driving the “obesity epidemic” in Australia. Read the rest of this entry »


Is obesity really caused by suburban sprawl?

Suburban sprawl is often linked with rising obesity – for example, see this submission to last year’s Urban Growth Boundary Review from Kelvin Thompson, Labor Member for the Federal seat of Wills, or this article in the Sydney Morning Herald.

The customary argument is that because the incidence of obesity is lower in the inner city where densities are higher, it follows that low density outer suburban development is the cause, or at least a very significant contributor, to obesity.

At first glance this seems to make some sense. For example, only 1.1% of workers in Melbourne’s outer suburbs walk to work, compared to 12.9% in the inner city.

But for all its faults, is it reasonable to put the blame for obesity on sprawl?  No, it isn’t reasonable. We would we better off focusing our energies on the real issues associated with sprawl rather than being distracted by sideshows.

The key reason is that what goes in our mouths is more important than how much we exercise. You have to walk the dog for an hour and a half, or cycle for an hour, to burn off the calories in just one Big Mac.

The inner city has a lower incidence of obesity primarily because the residents eat better. And they don’t eat better because of higher density but because they have higher incomes than residents of the outer suburbs and, importantly, higher levels of education. They are more likely to know about the importance of good eating and they are more likely to be able to afford to eat better food. They also have smaller households on average so it’s easier to cook healthy food at home rather than go out for fast food. Read the rest of this entry »