Paying the toll for traffic density
In King County, poor people and people of color more likely to live near packed, polluted roads
Seattle’s Chinatown-International District (ID) is known for The Chinatown Gate, which stretches across South King Street at Fifth Avenue South, and a pair of fiberglass dragons that snake around light poles.
Another, less visible characteristic sets the ID apart. The historic neighborhood has one of the highest rates of traffic density in King County and one of the county’s highest densities of people of color. It also possesses some of the county’s lowest rates of median income and English proficiency.
The ID is a stark example of something found all around urban King County: Low-income people, people of color and people with low levels of English proficiency tend to live in places with high traffic density, which can be harmful to one’s health.
“[These] findings confirmed that lower-income residents and people of color tend to experience more traffic pollution,” said Richard Gelb, performance measures manager for the county’s Department of Natural Resources and Parks.
Studies show that pollutants from roadways have a negative impact on a person’s health, including higher rates of asthma and cardiovascular disease, and may even be a risk factor in autism.
The connections between traffic, race, income and English proficiency are the focus of a recent report entitled “Traffic Density, Census Demographics and Environmental Equity in Housing.”
A geographic analysis of the county’s urban regions, the report was part of a mid-December policy briefing to officials in the public, private and nonprofit spheres engaged in the county’s Equity & Social Justice Initiative.
By the numbers
The local study, prepared by University of Washington graduate student Jill Schulte focused on the intersection of traffic and census data, but her findings have implications for those planning low-income housing.
Schulte employed a system called “weighted road density” (WRD), which calculated the average daily traffic volume on county roadways, as well as how far a specific census tract was from a major roadway. If a census tract was adjacent to an urban interstate, it received a WRD score of 100. If it was more than a mile from any major road, the region scored 0.
In the case of the ID, the neighborhood tied for the second highest WRD in urban King County with 84.9. Downtown Seattle/First Hill received a WRD of 87.3, and the West University District got 84.9.
But while downtown and First Hill may have more traffic, Schulte found that the ID ranked in the extreme in every variable examined in the report.
The ID has the region’s fifth highest percentage of people of color, the fifth lowest median income and the lowest level of English proficiency.
Studies that date back to at least 2002, and focus on regions as diverse as the Netherlands and Detroit have shown that traffic-related air pollution is a detriment to a person’s health. A study from Sweden showed a link between traffic noise and cardiovascular health.
In November, a study published in the Archives of General Psychiatry concluded that exposure to nitrogen dioxide and other air pollutants during a woman’s pregnancy and a child’s first year of life was “associated” with autism.
Beacon Hill produced a WRD score of 66.0, while Tukwila received 61.4, the highest city-wide average in the region.
The tiny town of Carnation, located in north central King County, received 3.03, the report’s lowest WRD score.
Even on Mercer Island, traffic and median income appear linked. Schulte said that although the island as a whole enjoys high rates for median income, the southern part of the island has low traffic density and more wealth. The northern tip of the island supports I-90 and has a lower median income.
Schulte examined 391 census tracts in the county based upon information from the 2010 U.S. Census.
She said that on average, as traffic density increased in a census tract, median income and English proficiency decreased. An uptick in traffic density was also aligned with higher percentages of people of color.
“What we have is a situation where the traffic [density] is not being equitably distributed among people in the county,” Schulte said.
But the report also highlighted some positive changes.
Schulte said that while people of color and low-income people do tend to live near more traffic-clogged areas, the link with income and race has declined in the past decade. In 2000, in urban King County neighborhoods to the east of I-5, such as the Central District, Beacon Hill, Auburn and Kent, people of color accounted for 75 percent or more of the population.
But by 2010, the demographics had shifted. People of color made up 50 percent to 75 percent of the population in the Central District and Beacon Hill. The percentage of people of color living near Tukwila, Renton and north of Bellevue, had increased. These shifts have moved some people of color to regions with lower WRD, which could mean they live in regions with lower rates of air pollutants.
English proficiency rates have also increased between 2000 and 2010 in most of the county.
Schulte said that one of the report’s goals was also to calculate typical traffic density near multifamily buildings, defined as structures with three or more apartments. While the county’s urban WRD was 29, the average score for multifamily dwellings was 41.1.
She said that the negative impacts of traffic could be mitigated by easy steps: bus and bike lanes, planting strips and buffer zones of trees or greenery set 50 feet from busy roadways.
In looking at data that stretched back more than a century, she found that multifamily buildings constructed after 1970 received higher WRD scores than multifamily housing built before the 1970s. In other words, the recent trend has been to build multifamily dwellings, including low-income housing, in neighborhoods with heavy traffic. “No one can figure out why,” she said. “It’s still a mystery.”
But Gelb, with King County, said that the mystery presents an opportunity.
He said policy decisions have not played a part in siting multifamily, low-income housing near areas with heavy traffic. But the county’s next steps will be to use the model Schulte created to craft policy decisions that reduce this tendency, thereby protecting the health of low-income people and people of color.
“Then we can understand the tools we can use to remedy this predicament,” Gelb said.
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