Study examines best car window combo in pandemic

  • Graphics from a study by UMass and Brown University researchers show how airflow can be affected within a car with two open windows. IMAGE COURTESY OF UMASS AMHERST PRESS OFFICE

  • Cars move along Woodhaven Blvd. as snow starts to fall Wednesday, Dec. 16, 2020, in the Queens borough of New York. AP PHOTO/FRANK FRANKLIN II

Staff Writer
Published: 12/26/2020 11:33:24 AM
Modified: 12/26/2020 11:33:13 AM

Travel has been discouraged during the pandemic, including being in a car with unrelated people. But if you have to take a taxi or a ride with Uber, are there any options for protecting yourself — and protecting the driver from yourself — outside of wearing a face mask?

A new study by a University of Massachusetts Amherst professor and other researchers reveals that rolling down car windows to provide airflow provides one option. But the study makes a surprising observation of which combination of windows might work best.

Varghese Mathai, who came to the university’s physics department this summer after teaching at Brown University, says a natural move by most people would be to roll down the window next to them. Thus a driver opens his or her window, while a passenger, sitting in the back of the car on the right, rolls down his or her window. 

But the study by Mathai and three of his former Brown colleagues — Asimanshu Das, Jeffrey Bailey and Kenneth Breuer — suggests a better option is doing the reverse: opening the right window in the front of the car and the left window in the back. Doing so, says Mathai, creates a cross-flow of air that acts like a barrier between the driver and the passenger and also helps flush away the airborne particles people exhale.

The scientists began their work, which was recently published in the journal Science Advances, in part to consider the problem presented every day by hundreds of millions of people traveling with unrelated drivers in taxis, Uber and other ride-sharing services. The study notes that airflow in such vehicles is best maintained by having all four windows down — three open windows can also be helpful — but that cold and rainy weather, or traveling at high speeds, generally precludes those options.

Having all the windows closed and then breathing air circulated by the car’s ventilation system is the worst option, Mathai notes.

He also makes clear that rolling down car windows “is not a substitute for a mask — wearing a mask is still the most important step you can take to protect yourself from airborne particles in any kind of confined space.” 

Given the limitations imposed by the pandemic, Mathai and his fellow researchers used computer simulations to do their work, and the UMass professor later used smoke visualization and field tests to back up those models. The scientists looked at a variety of configurations of closed and open windows; testing was done based on a typical passenger car traveling at 50 mph.

The exterior geometry of the car, which affects airflow, was based on a Toyota Prius, the study says.

Researchers concluded that with the left rear and right front windows open, air would flow into the car through the rear window, move around the passenger sitting on the right in the back of the car, and then exit the right front window — leaving a buffer of low-speed air circulating between passenger and driver that “help(s) to minimize the interaction with the driver in the front left position,” as the study puts it.

“The best thing you still can do is avoid travel and not share a car ride with someone who is not regularly around you,” said Mathai. “But if that’s unavoidable, there are some ways to reduce the risk” of contracting any pathogens.

Steve Pfarrer can be reached at







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