The physical shape of our urban environment has profound effects on human health. Urban design can determine which biological and chemical environmental hazards enter citizens’ bodies through air, water, or food. But the physical shape of our built urban environments directly affects public health, even absent chemical or biological contaminants.
When city planners and lawmakers decide whether to fund and build sidewalks, buses, highways, subways, light rail, bicycle lanes, or some combination, those decision makers influence how people travel. The shape of a built environment determines whether an individual can choose to lead an active lifestyle. No one can travel by bus if there is no bus.
Studies show that as individuals and populations decrease time spent in automobiles and increase time spent traveling by foot, bicycle, or even mass transit (those who take mass transit must walk to the station and thus walk more than car travelers), those individuals and populations encounter lower rates of obesity. Is this causation or correlation? Some U.S. studies hesitate to draw causation conclusions. A study by San Diego State University researchers found that children who walked to school had lower body mass indexes (BMI) than their peers. However, the study stated that the data were inconclusive as to whether walking to school lowered children’s BMI or whether children with lower BMI chose to walk to school. A study conducted by Planetizen declined to draw conclusions about whether walking or biking contributed to lowered rates of obesity for the sad reason that the sample size of walkers and bikers in the U.S. is too small.
When studies compare the U.S. to other countries with significant shares of active transportation users, the link between obesity and transportation modes becomes clear. A study in the Journal of Physical Activity and Health concluded that “there is an inverse association between active transportation and obesity rates in [the U.S., Canada, Australia, and European nations]. . . . The infrastructure, programs, and policies needed to increase walking and cycling are well known.” Similarly, a University of North Carolina study found that Chinese obesity rates increased 80% with car ownership.
Local transportation decision making in the U.S. is generally accomplished by local governments under local law. Federal government agencies have begun to take a more active role in urban sustainability issues and the White House has taken the initiative on childhood obesity. However, the federal government’s power is still generally limited to its persuasive power of the purse. Is there any way for the federal government to positively and comprehensively influence transportation mode choice? Could behavior-changing tax reform, such as a carbon tax, be the solution? Is there a way for the federal government to integrate transportation mode choice into its public health programs? These questions are becoming more urgent as America’s obesity epidemic grows.