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Driving to work as a public health problem

August 30, 2015

It turns out driving to work is indeed a public health issue. I did the math a hair more carefully, and over the entire population it looks like driving to work causes about twice as much 20% more early deaths than cigarette smoking (note that this is a difference of a difference; the overall annual mortality rate with smokers is 18% higher than not; the overall annual mortality rate with drivers is 21.5% higher than not). From OECD, Cycling, Health and Safety, pdf page 44, table 1.2:

“Relative risk expressed as a ratio of all cause mortality of cyclists compared to non-cyclists after controlling for confounding factors (age, gender, education, etc.) – e.g. a relative risk result of 0.70 indicates that a cyclist has a 30% reduction in risk of death compared to a similar non-cyclist.”

Location Relative mortality risk (cycling/non-cycling) Confidence interval Study
Copenhagen 0.72 0.57–0.91 Anderson et al, 2000
China 0.79 0.61–1.01 Matthews et al, 2007
China (HA) 0.66 0.40–1.07 Matthews et al, 2007
Finland 0.78 0.65–0.92 Hu et al, 2004
Finland (HA) 0.69 0.57–0.84 Hu et al, 2004

(HA) = “high activity”

A “relative mortality risk” of 0.79 (call it 0.8 for ease of math) means that in a given year a cyclist has only 80% of the risk of dying of a non-cyclist – or if you view the choice to not ride a bike as the abnormal behavior, a non-cyclist has a 25% (0.2 added to 0.8, 25% of 0.8) higher risk of death.

This is not as bad as smoking per-person – that about doubles (adds 100%) to your mortality risk – but only about 18% of the population smokes, and 86% of the population drives to work. Weighted by exposure, driving to work is a larger public health problem than smoking. (If 18% of population quit smoking, 18% of population cuts their 2x normal death rate in half, a 9% drop. If 86% of population quits driving to work and starts walking or biking, 86% of population cuts their death rate by 21%, an 18% drop.) (Math error: based on these numbers driving to work is the larger problem, but it is a 21.5% increase against an 18% increase.  From Calca:

.18 * 2 + (1-.18) * 1 => 1.18
.86 * 1.25 + (1-.86) * 1 => 1.215

Note that this says nothing about whether we make it easy for people to stop smoking or stop driving so much. Absolutely it is hard, I have friends and relatives with commutes that are completely impossible on a bicycle, or walking, or transit. We have chosen to make it hard for people to live healthier lives, and we should stop doing that. We need more transit from far-flung suburbs. We need safer streets to bike on, both in suburbs and in cities. We need greater density closer to work. Because our towns can’t necessarily afford greater density because of the property tax expense of serving all those extra people, we need to change how we fund things like education. Broken policy should be fixed, not used as an excuse.

3 Responses to “Driving to work as a public health problem”

  1. Opus the Poet Says:

    Hi doc! Interesting article coming at the issue from a completely different perspective, the damage drivers do to themselves. Could we add that on top of the lives lost from pollution caused by cars, and the indirect pollution caused by the supply chain required to keep cars fueled?

    • dr2chase Says:

      (You realize I’m not a “real” doctor, I hope.)

      The years of life lost to drivers through automobile-induced lack-of-exercise appears to be the largest cost of all. When you look at the various adjustments to life expectancy for other “preventable” causes, i.e., murders, suicides, car crashes, excess infant mortality, car crashes only cost us about 0.6 years in population-averaged life expectancy. Lack of exercise is apparently 1.7 years, maybe higher (it’s 2-5 years lost per car-commuting person, depending on gender, intensity of riding, etc).

      Crude math here: https://dr2chase.wordpress.com/2012/12/13/democrat-math/

      • Opus the Poet Says:

        I wasn’t sure about your medical degree, I just noticed we ran into each other on the same articles so frequently I thought for sure you would connect the same gravatars to the same name and come up with the same person.

        I just thought with the millions of early deaths attributed to all of the various forms of pollution caused by the supply chain for motor fuels that there would be a significant impact on the reduction of life expectancy due to automobilism.


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