We know that driving with the windows down is bad for you in terms of driving in an extremely polluted place, but a new study from Brown University indicates that driving with the windows up can greatly increase your chances of getting COVID-19 if you’re sharing a car with someone who is infected.
Researchers used computer models to simulate airflow and the dispersal of aerosols in a compact car’s cabin between two maskless people, a single rider and a driver. From SciTechDaily:
The study, by a team of Brown University researchers, used computer models to simulate the airflow inside a compact car with various combinations of windows open or closed. The simulations showed that opening windows — the more windows the better — created airflow patterns that dramatically reduced the concentration of airborne particles exchanged between a driver and a single passenger. Blasting the car’s ventilation system didn’t circulate air nearly as well as a few open windows, the researchers found.
“Driving around with the windows up and the air conditioning or heat on is definitely the worst scenario, according to our computer simulations,” said Asimanshu Das, a graduate student in Brown’s School of Engineering and co-lead author of the research. “The best scenario we found was having all four windows open, but even having one or two open was far better than having them all closed.”
The researchers also arranged the driver and passenger on opposites sides of the cabin (roughly sized to Toyota Prius specs) in order to keep the occupants a maximum distance apart, which still falls short of the 6 feet recommended by the Centers for Disease Control. They simulated the car traveling at 50 mph, with both driver and passenger breathing normally. It seems like common sense that driving with all of the windows down would cut down on the spread of the virus, but the science behind the models is still interesting. From SciTechDaily again:
Part of the reason that opening windows is better in terms of aerosol transmission is because it increases the number of air changes per hour (ACH) inside the car, which helps to reduce the overall concentration of aerosols. But ACH was only part of the story, the researchers say. The study showed that different combinations of open windows created different air currents inside the car that could either increase or decrease exposure to remaining aerosols.
Because of the way air flows across the outside of the car, air pressure near the rear windows tends to be higher than pressure at the front windows. As a result, air tends to enter the car through the back windows and exit through the front windows. With all the windows open, this tendency creates two more-or-less independent flows on either side of the cabin. Since the occupants in the simulations were sitting on opposite sides of the cabin, very few particles end up being transferred between the two. The driver in this scenario is at slightly higher risk than the passenger because the average airflow in the car goes from back to front, but both occupants experience a dramatically lower transfer of particles compared to any other scenario.
The simulations for scenarios in which some but not all windows are down yielded some possibly counterintuitive results. For example, one might expect that opening windows directly beside each occupant might be the simplest way to reduce exposure. The simulations found that while this configuration is better than no windows down at all, it carries a higher exposure risk compared to putting down the window opposite each occupant.
Naturally, it’s now winter weather in much of the country, which is partially why we’re seeing a huge spike in cases, according to CNN. People are gathering in enclosed spaces for the holidays while not changing their behavior to limit the spread of COVID-19. Researchers also point out that no model with two maskless occupants completely eliminated the risk of infection. Honestly, it’s best to skip the freezing, wind-blasted car ride altogether by following the CDC’s COVID-19 guidelines and staying home.
Not enough Americans are taking that advice to heart. As of this writing, the United States is nearing new 200,000 COVID-19 cases a day, according to CNN. The current death toll from COVID-19 is more than 282,310.