Does using public transport make the community healthier?

Perhaps another explanation is travellers with poor eating habits are over-represented among public transport users. For example, students tend to eat fast food because they're often out and about and have limited cash. In the US, this tendency would be reinforced by the high use of transit by very low income groups.

The authors note that good access to public transport might lead to some short trips that would otherwise be taken on foot being replaced by train, bus or tram i.e. some travellers walk less in total when there's a faster option available, like the frequent free trams in Melbourne's CBD.

For example, see this comment on an unrelated topic by reader Waffler.

I have a yearly Myki and find it is the same with PT. I don't care how much I use it and hop on the tram or bus to travel only a stop or two if it is handy (yeah I know I am lazy!) because it doesn't cost me any extra.

The authors also suggest the exercise benefits of walking to the station might be offset for some people by the mental stresses – e.g. greater anxiety – of travel by public transport. This might also be linked to poor eating habits.

Finally, it might be that the sorts of destinations that driving makes accessible provide on average a degree of walking and exercise that offsets some or all of the foregone walk to the local station e.g. regional shopping malls, regional parks, beach. Not all drivers have basement car parks at work either.

These are only conjectures and some seem more plausible than others. As noted, I can't say if the paper supports its findings satisfactorily or not. This is only one study so it wouldn't be prudent to put too much weight on it.

My view – which I've set out a number of times before – is that far too much weight is given to the influence that the physical environment has on health outcomes.

As I noted here, I think Henry Overman, Diego Puga and Mathew Turner were right when they pointed out in their paper, Fat city: questioning the relationship between urban sprawl and obesity, that sorting rather than causation is the primary mechanism that drives observed differences within cities on many socioeconomic variables.

It follows immediately from our results that recent calls to redesign cities in order to combat the rise in obesity are misguided. Our results do not provide a basis for thinking that such redesigns will have the desired effect, and therefore suggest that resources devoted to this cause will be wasted. The public health battle against obesity is better fought on other fronts.

Update 26 August 4:30 pm. This is how silly it gets; just published today: Miracle tram to cure obesity.