Planting trees and bushes along highways can significantly cut local motor pollution levels, study finds

If you’re a frequent motorist in India, you probably understand the value of roadside greenery more than anybody else. In addition to aesthetically elevating the drab jungle of concrete and asphalt quite fantastically, a lush bit of traffic intersection canopy is often the last shield against the blistering Indian Sun for many bikers.

However, amidst the expanding concrete highways of India, roadway greenery is fading, succumbing to the pressures of development and pollution. It is common to see plants at traffic medians and islands wilting away for lack of care, or even destroyed by stray cattle which use these spots as drive-through diners. Not only is this terrible from an ornamental standpoint, a new study has found that these plants also play a crucial role in mitigating the harmful effects of motor vehicle emissions.

To understand the impact of trees and bushes on reducing air pollution, researchers meticulously sampled air quality at five sites on a US highway, comparing areas with natural or ornamental vegetation to similar sites devoid of greenery. The results were striking: the roads adorned with plants observed a 37% reduction in soot and a 7% reduction in ultrafine particles.

The researchers believe this is because trees and bushes create a large surface area onto which small particles adhere, effectively trapping pollutants and preventing them from dispersing into the surrounding environment. This natural filtration system, augmented by the strategic placement of greenery, could offer a tangible solution to the pressing challenge of elevated pollution levels near roadways.

However, study author Roby Greenwald is quick to caution against viewing verdant roadways as a panacea for all woes associated with motor vehicle emissions. While it significantly reduces particulate air pollution, it does not adequately address carbon dioxide emissions or ozone pollution — greenhouse gases that are helping the planet boil over to dangerous levels.

"We should plant more trees along roadways because they provide benefits that go beyond aesthetics," Greenwald explains. "But 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."

Air pollution, a silent killer often associated with respiratory diseases and cardiovascular ailments, knows no boundaries. Further, many Indian schools and colleges are strategically placed near highways, which not only heightens their students’ risks of exposure to harmful pollutants, but also puts them at greater road accident risk.

The urgency to address this issue becomes increasingly apparent as scientific evidence continues to mount, linking motor vehicle pollution to conditions such as asthma, chronic bronchitis, lung cancer, and heart attacks. Municipalities must improve air quality by investing in public transportation infrastructure, promoting active transportation modes such as cycling and walking, and implementing policies that prioritise environmental sustainability.

The findings of this research have been published PLoS One and can be accessed here.