Walking and clean air

New study compares 'walkability' in Vancouver neighborhoods with local levels of air pollution

By Rick Moore

Determining which neighborhoods encourage walking and which parts of a city are beset by pollution seems easy enough. Avoid the core downtown areas and look for a walkable stretch in the suburbs, right?

It's a bit more complicated than that. A new study done for the metropolitan area of Vancouver, British Columbia (host of the 2010 Winter Olympics) , compares neighborhoods' "walkability"-the degree of ease for walking-with local levels of pollution, and reveals some interesting findings. Among them: some neighborhoods might be good for walking but have unexpectedly poor air quality.

The study, published in the November issue of Environmental Health Perspectives, is the first study to explore interactions between neighborhood walkability and air pollution exposure. The researchers include Julian Marshall, an assistant professor in civil engineering at the University of Minnesota's Institute of Technology, and University of British Columbia faculty Michael Brauer and Lawrence Frank.

Researchers assigned a walkability score by analyzing four attributes of neighborhood design: population density, intersection density, land-use mixing (e.g., residential and retail), and ratio of land area devoted to shopping versus parking. More walkable neighborhoods tend to have mixed land uses, with stores and shops within walking distance of houses. Areas with low intersection density contain more circuitous road networks, making them less walkable.

Marshall and colleagues found a complex interplay between neighborhoods' walkability and air pollution. Downtown neighborhoods are generally more walkable but have high levels of nitric oxide - a marker of motor vehicle exhaust. Suburban areas, on the other hand, tend to be less walkable but have their own issues with pollution; namely, higher concentrations of ground-level ozone. Elevated ozone concentrations tend to occur in the suburbs because ozone takes time to form. During that time, air masses often have migrated away from the downtown area.

"The built environment - how we choose to structure our infrastructure - influences how we act, and [consequently] our health," Marshall says. "If there's no sidewalk, you're less likely to walk."

"Research has shown that exposure to air pollution adversely affects human health by triggering or exacerbating a number of health issues such as asthma and heart disease," says Marshall. "Likewise, physical inactivity is linked to an array of negative health effects including heart disease and diabetes. Neighborhood design can influence air pollution and walkability; more walkable neighborhoods may encourage higher daily activity levels."

Fortunately for Vancouver, the researchers found some "win-win" neighborhoods - those that are both walkable and have lower levels of air pollution - but they account for only 2 percent of the areas they studied. And census data shows that people with relatively high incomes live in those neighborhoods, suggesting that they are desirable places to live and perhaps unaffordable to many. Interestingly, neighborhoods that fare poorly for both walkability and pollution tend to be in the suburbs and where generally middle-income families make their homes.

Since the data for the study are particular to Vancouver, Marshall can only speculate as to how the Twin Cities metropolitan area would fare when evaluating the intersections of walkability and pollution. But he has some guesses on where some win-win neighborhoods would be; namely, the Macalester-Groveland area on the west end of St. Paul and portions of south Minneapolis near the chain of lakes.

"It's reassuring that you can split the difference - avoid both types of pollution and still get a walkable neighborhood," Marshall says.

Planning for the future

The study's findings suggest the need for urban planners to consider both walkability and air pollution, while realizing that certain neighborhoods are prone to high levels of pollution-either nitric oxide or ozone.

"There is urban planning now that focuses on walkability and exercise-friendliness," Marshall says. But while that idea is on planners' minds, "the connection to air pollution isn't as much."

Fortunately, addressing walkability might naturally lessen air pollution. Creating neighborhoods that allow for alternative transportation modes such as biking, walking, and public transit is one way to reduce motor vehicle emissions, the study suggests.

It's about "allowing people to live in a less car-dependent neighborhood, if they wish to," Marshall says.

Sometimes that's easier said than done. Urban planners often face zoning laws and regulations, including height restrictions for buildings and minimum parking requirements for retail establishments.

"The built environment - how we choose to structure our infrastructure - influences how we act, and [consequently] our health," Marshall says. "If there's no sidewalk, or if destinations like shops and restaurants are miles away, you are less likely to walk there."

In the future, the researchers hope to investigate changes over time in walkability and pollution, and also study other urban areas to see how spatial patterns may differ.

To read the study in its entirety, visit the Environmental Health Perspectives Website.