Critical Mass – for health and safety?

critical massnoun – An amount necessary or sufficient to have a significant effect or to achieve a result.

massnoun – Bulk; magnitude; body; size.

Most physicists think of “critical mass” very differently than most bicyclists. I wonder what Albert Einstein thought of the term since he wasn’t just a great physicist; when asked about his Theory of Relativity he once said, “I thought of that while riding my bicycle.” In addition to a very fun Friday evening ride, the term also relates to the “safety in numbers” effect that we enjoy when more people ride more bikes more often. To quote our own NZTA:

“It was found that a noticeable ‘safety in numbers’ effect exists. Generally, the overall increase in cycle and pedestrian accidents was not substantial and the crash rate per cyclist and pedestrian reduced with increases in their numbers.”

“New Zealand has found that the crash rate per cyclist reduces as the cycle volume increases; the ‘safety in numbers’ effect.”

This is consistent with studies from several other countries. Even if NZTA doesn’t use the term “critcal mass”, they still seem to understand that more people riding more bikes more often means that everyone on a bike is safer. How much safer? Check out this chart from the Netherlands, comparing bicyclists’ deaths to bicyclists’ travel distances…

safety in numbers
This is what an "inverse correlation" looks like. As a native English speaker, spoken Dutch sometimes sounds like it's being spoken backwards, but after translating this chart from the original Dutch the inverse correlation is still the same.

The solid line shows bicyclists killed per BILLION kilometers of travel.The dashed line shows kilometers bicycled per person. In the mid/late ’70s when bicycling popularity was lowest (in the Netherlands), bicycling was most dangerous. Since then bicycling has become popular once again and safety has improved. Combine the “safety in numbers” effect with the right infrastructure and the right attitudes, and bicycling in the Netherlands is safer than it’s ever been.

There’s another “inverse correlation” that applies to bicycling, has to do with mass, and it’s critical to understand this when making health, safety and transport decisions on a national scale. And it makes for nice charts. This is the “mass” of bicyclists (and people who walk and use public transport) being lower than the “mass” of motorists. I’m talking about obesity.

obesity vs active transport
Shocker: The less bicycling and walking people do, the fatter they get.


obesity vs active transport
Different methods of measurement, same trend.

Yup. Believe it or not, there’s an inverse correlation between active transport and obesity. International comparisons of obesity rates are difficult to make because different methods of measurement are used, but NZ is consistently on the top-ten list of the world’s fattest countries, and often in the top-three. But being overweight is more than just a social stigma…

“In 1991 the direct costs of obesity to New Zealand’s health care system were conservatively estimated at $135 million per year, or 2.5 percent of health expenditure for that year. On this basis the figure for 2000/01 would have been at least $247.1 million, and it will be higher today.” –

“In an earlier (2003) study carried out jointly by the Ministry of Health and the University of Auckland, higher than optimal BMI was estimated to contribute to approximately 3200 deaths in New Zealand in 1997, mostly through type 2 diabetes, IHD and stroke. This burden will be even higher today given that the mean BMI of the adult population has increased since 1997.”

Those numbers have only gotten worse in the last ten years, but I haven’t been able to find out exactly how much worse. If anyone knows where to find more recent data on NZ’s obesity costs (economic, social or other costs), please post it in the comments.

OK, that says that being overweight “contributed to”, rather than caused, 3,200 deaths in NZ in 1997. Still, it provides some perspective to point out that that’s over six times more than the 532 fatalities caused by motor vehicles in NZ that same year (of those 532 deaths caused by motor vehicles, 12 {2.3%} were bicyclists and 47 {8.9%} were pedestrians). To put the monetary costs of obesity into perspective, ACC’s total costs for motor vehicle injuries and deaths in 2000/2001 was about $207M. While the long-term trend in transportation safety seems to be improving, the obesity epidemic keeps getting bigger.

Riding bikes saves lives, saves money. And it’s fun! The risk isn’t riding a bike, the risk is NOT riding a bike! (an article here and peer reviewed studies here and here)

So what can New Zealand do? Start by diverting some funding from road building and using it to fund alternatives to private motor vehicle transportation. The more we put into public transport, bicycling and walking, the more people will happily leave their cars at home. The funny thing is that this will not only make walking and bicycling safer and more appealing, but will also increase the longevity and, perhaps more importantly, the quality of life for those who take up alternatives to private cars (not to mention the economic and environmental benefits to the country).

What can Wellington (and other cities) do? Start promoting bicycling! Now! Wellington seems reluctant to do this directly, until after they install more bike lanes, more bike parking, etc. The intent seems reasonable; that more/better bicycling infrastructure makes bicycling safer, and they don’t want to promote bicycling (as such) until better/safer infrastructure is in place. While there’s some merit to this, they can encourage people RIGHT NOW to get on their bikes, and just by doing that they make bicycling safer for everyone.

For safe bicycling: Get on your bike!

For staying healthy and living longer: Get on your bike!



2 thoughts on “Critical Mass – for health and safety?

  1. Pingback: Friday roundup | Bicycle Victoria Blog

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