Tips For Minimizing The Spread of COVID In Cars

As the pandemic drags on, you may find yourself in a situation when you have to ride in a car, or in a taxi, Uber or Lyft—or in your own or someone else’s vehicle—with someone who isn’t in your coronavirus bubble. 

New research reported in The New York Times, How To Literally Drive the Coronavirus Away, suggests some practical data-based tips for minimizing the spread of COVID in cars. The advice in the NYT piece is based on empirical research recently published in the AAAS publication Science Advances. 

These AAAS research findings can be helpful to bear in mind in a number of situations: Even if you are very COVID-cautious, you might need to drive a friend to a doctor’s appointment, take a taxi or car service to an airport, or decide to drive to a nearby park with a neighbor. So read this carefully.

What we already knew about COVID and cars

Previous research has shown that riding or driving in an enclosed space increases the risk of exhaled droplets and aerosols transmitting COVID-19. In fact, it is estimated that the viral load inside a car cabin for drives as short as 15 minutes can remain in the vehicle for up to three hours. And Dr. Richard Corsey, an air quality expert at Portland University, told the NYT that a 20-minute car ride with an infected individual, even someone asymptomatic, can be riskier than sharing a classroom or dining in a restaurant with that person for more than an hour.

As a result, and consistent with public health guidelines, many individuals (and transportation companies) are exercising common sense precautions including limiting the number of passengers in a vehicle, requiring masks for occupants, and opening windows—although the latter can be challenging in cold climates during winter months. But there has been some ambiguity about which windows to open.

Industry has also embraced some procedures to limit airborne transmission in vehicles. For example: 

• The New York City Taxi and Limousine Commission suggests drivers use the vehicle’s vents to bring in fresh outside air and/or lower the windows. It also suggests avoiding use of recirculated air.

• UBER passengers must agree to sit in the back seat with the windows open for ventilation. 

• Lyft passengers and drivers are asked to, when possible, leave windows open and avoid recirculated air.

New science-based findings

Using computer simulation models, this quantitative AAAS study (co-authored by Varghese Mathai, Asimanshu Das, Jeffrey A. Bailey and Kenneth Breuer) specifically examined how airflow patterns affect the transmission of COVID in cars. The study data is based on two people driving in a five-seater car (which is close to the average occupancy and seating configuration in passenger cars in the United States).

The researchers found that “an airflow pattern that travels across the cabin, farthest from the occupants, can potentially reduce the transmission risk” and offered recommendations about how this could be achieved.

5 tips for riding more safely in cars during the COVID pandemic

Here are the tips gleamed from this and other research:

• There’s safety in (low) numbers: Driving alone is safest; increasing the number of passengers increases the risk of transmission.

• Wear a mask: If you do need to ride with one or more other people, wear a mask. Although masks are useful, micrometer size particles can still escape when breathing, talking, coughing or sneezing.

• Maintain physical distance: With the driver in the front left-hand seat, maximal physical distance is achieved when the passenger is seated in the rear right-hand seat.

• Open windows: Open windows markedly improve air flow compared to all-windows-closed with air-conditioning (the least effective option). 

• Open the windows correctly: Although it seems counter-intuitive, opening the two windows farthest from the occupants (front-right and rear-left, respectively) gives better protection to the passenger. But opening the two windows adjacent to the driver and passenger is better than the all-closed-windows scenario. No data is available on partially open windows.

COVID transmission in cars: The bottom line

A report on the same study in Science Daily notes, “…researchers stress that there’s no way to eliminate risk completely — and, of course, current guidance from the U.S. Centers for Disease Control (CDC) notes that postponing travel and staying home is the best way to protect personal and community health.”

Again, if you must drive with someone else: Try to fully open the two windows farthest from the occupants (FR and RL, respectively).

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Additional information

• CDC Guidance on Transportation/Personal Vehicles 
• NY Times: How To (Literally) Drive the Coronavirus Away 

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