Trees Along Highways Don't Just Make the Drive Prettier

It's arguably more pleasant to drive along a highway lined with trees and bushes versus one that lacks greenery. A new study finds the upside isn't just aesthetic. Georgia State University researchers report in a study published in PLoS One that vegetation along highways significantly reduces the air pollution highway traffic causes. To arrive at that conclusion, they took air-quality samples at five sites along metro Atlanta interstates and highways in the summer: two with vegetative barriers including magnolia trees and water oaks, one with a solid barrier, and two with only a chain-link fence.

Their modeling allowed them to consider factors like wind direction, traffic volume, and distance to the highway. They found the vegetative barriers returned the greatest reduction of traffic-related air pollution: a 37% reduction in soot and a 7% reduction in ultrafine particles. The authors note that roughly 45 million Americans live, work, or go to school within 1,000 feet of a major highway, "which constitutes a sizable amount of the population being at risk." As a press release notes, motor vehicle pollution has been linked to asthma, chronic bronchitis, lung cancer, and heart attacks.

In lead author Roby Greenwald's view, the findings won't lead to a total solution, "but they can help reduce the severity of the problem," he says. He also points out that roadside vegetation—which provides a large surface area onto which small particles can stick—doesn't reduce carbon dioxide emissions or ozone pollution. "I don't want to give anyone the impression that we can solve all of the problems associated with motor vehicle emissions simply by planting trees." (A key figure in the "plant trees" movement has a new message.)