As it is not always practical to have all windows open, especially in the dead of winter, Dr. Mathai and his colleagues have also modeled several other options. They found that while the seemingly more intuitive solution – getting the driver and passenger to open their windows – was better than keeping all windows closed, an even better strategy was to open the windows opposite each occupant. This configuration allows fresh air to enter through the left rear window and exit through the right front window and helps to create a barrier between the driver and the passenger.
“It’s like an air curtain,” said Mathai. “This releases all the air that is released by the passenger and also creates a region of strong wind between the driver and the passenger.”
Richard Corsi, an air quality specialist at Portland State University, praised the new study. “What they did is very sophisticated,” he said, although he warned that changing the number of passengers in the car or the speed of driving could affect the results.
Dr. Corsi, co-author of the article with Dr. Allen last year, developed his own model of coronavirus aerosol inhalation in various situations. Their results, which have not yet been published, suggest that a 20-minute drive with someone who is emitting infectious coronavirus particles can be much more risky than sharing a classroom or restaurant with that person for more than an hour .
“The focus has been on over-spreading events” because they involve so many people, he said. “But I think what people sometimes don’t realize is that over-spreading events are started by someone who is infected who comes to that event, and we don’t talk often enough about where that person was infected.”
In a follow-up study, which has not yet been published, Dr. Mathai found that opening the windows in half seemed to provide the same benefit as opening them fully, while breaking them in just a quarter of the way was less effective.
Dr. Mathai said the general findings were likely to be valid for many four-door, five-seater cars, not just the Prius. “For minivans and pickups, I would still say that opening all windows or opening at least two windows can be beneficial,” he said. “Besides, I would be extrapolating too much.”