Scientists Devise Roadside Barriers to Limit Air Pollution from City Traffic

(Inside Science) -- Curved barriers fitted along city roads could keep the air pollution caused by vehicles away from pedestrians, cyclists and children playing nearby, according to a new study. They’ll continue to protect people even as vehicles emit less from their engines -- and even if the traffic on our roads becomes fully electric and cars stop producing exhaust.

“There are things we can do right now to improve air quality in some urban landscapes,” said urban ecologist Tilly Collins at Imperial College London. “We can use the shaping of our urban structures to deflect vehicle-generated pollution away from people.”

Collins is the lead author of a study published in Cities and Health describing the new barrier design.

She started thinking about the pollution from city roads when she visited a West London schoolyard where her children were playing. Although it was walled off from an adjacent city road, the air on the playground side of the wall still smelled strongly of traffic pollution, and the haze of it was visible. She started to research why the barrier didn’t keep the air clear.

“What happens is that some air pollution comes over and it eddies around behind the wall,” she said during an online presentation this week. “You can get areas where you get just as much air pollution on the other side of the wall as on the traffic side of the wall, because the vortices and the eddies it creates hold it there.”

Further research revealed that even though vehicles are cleaner than they used to be, exhaust emissions are just part of the problem.

Studies show pollution from exhaust fumes is falling as measures to clean up engines and fuels start to work. But a “strong remnant” of air pollution from road traffic remains, caused by the abrasion of the road surface itself and the wear on vehicle tires and brakes -- problems estimated to cause hundreds of thousands of premature deaths every year, and which will still be problems even when traffic produces no exhaust.

“These are quite heavy particles that lurk around our roads,” Collins said. “Even with the transition to electrification, we are still going to experience these.”

To address the problem, Collins and her colleagues have designed curved barriers, just a few feet high, to prevent eddies of air pollution from forming on the pedestrian side and to deflect the pollution back onto the road. This would increase pollution above the roads themselves, but Collins noted that unlike people near the road, cars and trucks have air filters to deal with the problem.

The new barriers, probably made from perforated steel, could be inexpensively “retrofitted” along existing city roads to improve the quality of the air beside them. And while there will be some costs for installing them, those will be easily outweighed by their benefits to human health, she said: The World Health Organization estimates outdoor air pollution causes 4 million deaths every year, and pollution from traffic makes up a large part of that.

Collins envisioned that the roadside barriers could also act as scaffolds for plants like ivy, increasing “green” infrastructure throughout large cities.

“The fact that we can include ‘greening’ is important to me,” said Collins, who worked as a tree surgeon before becoming a scientist. “I strongly believe that seeing green makes us happier.”

For transportation scientist Fiona Rajé at Manchester Metropolitan University in the U.K., the proposed barriers underline an opportunity to introduce solutions during the lull in traffic pollution caused by the COVID-19 lockdowns.

“We urgently need to address the impacts of air pollution as it rises towards pre-COVID levels,” she said. “This research contributes to our understanding of potential local solutions to global challenges.”

Climate scientist Eugene Cordero of San Jose State University in California and the Mineta Transportation Institute noted that further studies are needed to measure how effective the barriers can be at preventing traffic pollution. However, “this is the exact kind of applied research that we need to be considering in terms of public health, especially around urban areas,” he said.

Cordero is an avid cyclist, and he sees potential for the design to separate bicycle lanes from vehicle traffic while improving the air quality above them.

“If you could combine it by making cyclists feel safer too, then I could see this mechanism making sense,” he said. “I think the cycling community would find this interesting.”