If you’ll be driving on busy roads this holiday weekend, you might want to take note of a new study about traffic and air pollution: The research, conducted by the University of Surrey in the United Kingdom, suggests that keeping car windows closed and fans switched off while stuck in slow-moving traffic jams can reduce your risk of exposure to toxic fumes by up to 76 percent.
Using the fan’s or air conditioner’s “recirculate” option ranked second best when researchers tested five different ventilation settings, and they say that this can also be a good choice for reducing exposure to pollutants.
The findings aren’t just applicable to weekend or vacation driving; in their paper, the study authors note that daily commuting time has increased over the years in Britain, where people spent about an hour each day driving to and from work in 2013. The numbers are similar in the United States: Americans spend an average of nearly 52 minutes on their round-trip commutes, according to 2013 government data.
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Air pollution is considered among the top 10 health risks faced by humans by the World Health Organization, which attributes it to 7 million premature deaths a year. It’s an especially big problem in urban cities, the study authors write, where traffic-light intersections are known as “pollution hotspots that contribute disproportionately higher to overall commuting exposure.” Last year, the same researchers showed that drivers stuck at traffic lights were exposed to up to 29 times more harmful pollution particles than those driving in free-flowing traffic.
In London, they note, air pollution is estimated to kill more than 10 times the amount of people as automobile accidents. And in the United States, exposure to ambient particulate matter is the eighth leading cause of death.
The researchers wanted to study the effects of different vehicle ventilation systems on a driver’s or passenger’s exposure to both fine and coarse particulate matter—two types of pollution consisting of vehicle exhaust, ozone, and other toxins prevalent the air. So they performed readings both inside and outside a 2002 Ford Fiesta in Guildford, a “typical UK town” of about 137,000 residents, at busy three- and four-way traffic intersections during winter-season rush hours.
Five scenarios were studied, with different combinations of windows (open or closed), fan (off, partial speed, or full speed), and heat (off, low temperature, or high temperature). When it came to pollution exposure, results varied widely depending on the ventilation.
When driving with the windows open, particulate matter readings in the car were equal to those outside of the car. When the windows were rolled up and the fan was switched off, however, exposure to particulate matter was reduced by up to 76 percent.
“Where possible and with weather conditions allowing, it is one of the best ways to limit your exposure by keeping windows shut, fans turned off and to try and increase the distance between you and the car in front while in traffic jams or stationary at traffic lights,” said lead author Prashant Kumar, Ph.D., in a press release. “If the fan or heater needs to be on, the best setting would be to have the air re-circulating within the car without drawing in air from outdoors.”
Kumar’s study isn’t the first to suggest that hitting the recirculate button is a good option while stuck in traffic; a 2013 study from University of California researchers also came to similar conclusions. This was, however one of the first studies to test several different ventilation options head-to-head at busy urban intersections, specifically.