Tip Sheet

COVID-19 study: There’s a proper way to have car windows down with passengers onboard

Because science
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“If you’re traveling with passengers, roll your windows down to improve airflow inside the vehicle.”

Yes, yes. We’ve all heard this COVID-busting tip countless times already, but according to a December 2020 study by students from Brown University in Providence, Rhode Island, there’s a proper way to go about this.

Using computer models based on a Toyota Prius traveling at 50kph to simulate in-vehicle airflow, the study found that choosing exactly which windows to open depending on where passengers are positioned creates different air currents that can “increase or decrease exposure to remaining aerosols.”

One scenario the model tackled was opening the window beside each occupant in a car carrying two people sitting on opposite sides of the cabin. At first glance, this seems like an obvious way to go about limiting aerosol transmission between passengers. Findings showed, however, that this strategy leads to higher exposure risk (though still less than having no windows open at all) than opening the windows opposite of each passenger.

According to the study, the reason for this is that air outside the car has more of a tendency to enter via the rear windows where air pressure is higher—something to keep in mind when the weather doesn’t permit having all your windows rolled down. Look:

“When the windows opposite the occupants are open, you get a flow that enters the car behind the driver, sweeps across the cabin behind the passenger, and then goes out the passenger-side front window,” Kenny BreuerBrown University engineering professor, said.

“That pattern helps to reduce cross-contamination between the driver and passenger.”

Again, though, it’s important to note that a setup with any car windows down is better than having them all up and relying on your A/C system.

“Driving around with the windows up and the air conditioning or heat on is definitely the worst scenario, according to our computer simulations,” research co-lead author Asimanshu Das stressed.

“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.”

You can check out the study in its entirety here. So, how do you go about traveling by car during COVID times? With your windows down and your masks on, we hope.

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