This is the worst thing you can do in a car when it comes to spreading COVID-19 faster

Photo: Antonio DiCaterina

When discussing risks associated with coronavirus transmission, we rarely appraise automobiles with the same scrutiny as we do indoor establishments.

There are certainly relevant differences but not enough to dull caution, a new study published in the journal Science Advances posits.

In it, a team of researchers from Brown University determined that passengers traveling inside a vehicle with the windows up significantly increase their risk of contracting the novel coronavirus (SARS-CoV-2).

“Transmission of highly infectious respiratory diseases, including SARS-CoV-2, is facilitated by the transport of exhaled droplets and aerosols that can remain suspended in air for extended periods of time. A passenger car cabin represents one such situation with an elevated risk of pathogen transmission,” the authors wrote in the report. “Here we present results from numerical simulations to assess how the in-cabin microclimate of a car can potentially spread pathogenic species between occupants, for a variety of open and closed window configurations.”

In order to thoroughly gauge automobile risks, the authors used a simulated car that held two people inside—with the second passenger sitting in the back seat on the opposite side from the driver.

The authors note that this particular seating arrangement is the safest way to travel, as it allows the maximum amount of physical distance between two people sharing a vehicle. It should be noted that the researchers based their model car on a Toyota Prius.

The computer model-simulated airflow around and inside a car moving at 50 miles per hour, in addition to the movement of viral particles coming from both the driver and the passenger at varying concentrations.

“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,” explained Kenny Breuer, a professor of engineering at Brown and a senior author of the research in a media release. “That pattern helps to reduce cross-contamination between the driver and passenger.”

The models employed by the researchers revealed that open windows facilitate airflow patterns that reduce the concentration of airborne viral debris disbursed between a driver and a single passenger. This worked much better than standard car ventilation systems.

The worst thing a driver can do, with respect to coronavirus transmission risk, is operate their vehicle with the windows up and the air conditioning or heat on.

Conversely, driving with all four windows open was deemed to be the safest way to drive according to the new research.

Of course, it’s nearly impossible to adhere to the six-foot distance rule established by the Centers for Disease Control and Prevention while sharing a vehicle with someone else, which is why the authors of the new report stress that there is no way to completely eliminate transmission risk while driving.

“An airflow pattern that travels across the cabin, farthest from the occupants can potentially reduce the transmission risk. Our findings reveal the complex fluid dynamics during everyday commutes, and non-intuitive ways in which open windows can either increase or suppress airborne transmission,” the authors concluded.