PUBLIC HEALTH
January 7, 2010

Leave Your Car At Home: Walk

A study shows how reducing road traffic by walking or biking can cut carbon emissions by half and make people healthier.

A study published in the Lancet offers simple advice on how city dwellers can fight global warming: drive less, walk and bike more. Not only will this cut down on carbon dioxide emissions, it will also improve people's health in several ways.

More than half of the world's population lives in cities.

Global warming seems huge and impersonal. Individuals who are concerned about it rarely consider actions they can personally take to halt or slow it. They have little leverage with their utility company or over their country's industrial practices. They don't set public policy, and if they work for a company, generally have little control over its energy usage. But people travel and travel accounts for about one−quarter of all carbon dioxide emissions. How people travel can make a difference.

The health benefits came mainly from increased personal exercise, though lowered air pollution and fewer road fatalities also played a part.

Road traffic accounts for about three−quarters of all travel−related carbon dioxide and continues to rise. Less road travel means less carbon dioxide.

The researchers made certain mathematical predictions about life in 2030 in two different cities: London (a large city in a highly motorized country) and Delhi, India (a large city in a country that is rapidly becoming motorized). They looked at four different scenarios: first, business as usual—no policies to reduce greenhouse gases in effect. Second, a scenario where policies focused on lowering auto emissions, mainly through improved mileage cars. Third was a scenario with less car travel and more walking and biking. Fourth was a scenario with both lower emission cars and increased walking and biking—the combination scenario. The amount of carbon dioxide produced and the effects on people's health were calculated for each of these four scenarios. All carbon dioxide emissions were compared to the amount emitted in 1990.

In 2030 London, a policy of doing nothing led to a 4% increase in carbon dioxide emissions. Less car travel lowered carbon dioxide slightly better than improved auto emissions did (a 38% drop vs. a 35% drop). In 2030 Delhi, carbon dioxide emissions rose 526% under the business as usual scenario. They rose 447% under the improved emission scenario but only 235% under the less car travel scenario. Naturally, the combination scenario worked best in both cities.

When it came to health, the benefits from less car travel were about 45 times greater in London and 7 times greater in Delhi than the health benefits from improved auto emissions. The health benefits came mainly from increased personal exercise, though lowered air pollution and fewer road fatalities also played a part. The benefits included a decrease in heart disease, strokes, diabetes, depression, dementia and certain types of cancer, especially breast cancer.

All these numbers are based on fairly uncertain projections and estimates. They suggest that while improved auto emission standards will be useful in lowering carbon dioxide emissions, less car travel and more biking and walking will both lower carbon dioxide emissions and lead to a healthier population. Just how large the effect will be is something for the number crunchers to argue about.

The article also points out that for urbanites to bike and walk more, cities have to be made more pedestrian and bike friendly. Right now, city roads and intersections are laid out for the convenience of car traffic and are often dangerous for anyone not sitting behind the wheel of an SUV. In the past, the United States has been more likely to monetarily bail out their auto industry than to build city infrastructure that is safe for bikers and pedestrians. That attitude must change if biking and walking are to become as attractive as car travel.

Another study, published in an early online version by the Lancet on November 25, suggests a second way individuals can help lower carbon dioxide emissions: people who eat a lot of animal products (mainly meat) can eat less of them. This lowers energy use because the production of meat uses much more energy and generates more carbon dioxide than the production of plant−based foods does. This is likely to have health benefits too, as high meat consumption increases the risk of cardiovascular disease.

The article on greenhouse gas emissions and health changes caused by different urban transport scenarios was published in the December 5, 2009 issue of the Lancet.

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