Since it is not always practical to have all windows wide open, especially in the dead of winter, Dr. Mathai and his colleagues also modeled several other options. They found that the most intuitive solution – letting the driver and passenger each roll down their own windows – was better than keeping all the windows closed, an even better strategy was to open the windows facing each occupant. This configuration allows fresh air to flow in through the rear left window and through the front right window, creating a barrier between the driver and front passenger.
“It’s like an air curtain,” said Dr. Mathai. “It flushes out all of the air that is released by the passenger and creates a strong wind region between the driver and front passenger.”
Richard Corsi, air quality expert at Portland State University, praised the new study. “It’s pretty nifty what they did,” he said, although he cautioned that changing the number of passengers in the car or the speed of travel could affect the results.
Dr. Corsi, co-author of the report with Dr. Allen in the last year has since developed his own model for inhaling coronavirus aerosols in various situations. His results, which have not yet been published, suggest that a 20-minute drive with someone emitting infectious coronavirus particles can be much riskier than sharing a classroom or restaurant with that person for more than an hour.
“The focus was on superspreader events,” because they affect a lot of people, he said. “But I think what people miss sometimes is that superspreader events are started by someone who is infected and come to that event, and we don’t talk enough about where that person got infected.”
In a follow-up study that has not yet been published, Dr. Mathai found that opening the windows halfway gave about the same benefit as opening them fully, while cracking them only a quarter of the way they opened was less effective.
Dr. Mathai said the overall results would most likely apply to many four-door, five-seat cars, not just the Prius. “For minivans and pickups, I would still say that opening all the windows or opening at least two windows can be beneficial,” he said. “In addition, I would extrapolate too much.”