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To wear a mask, or not, on public transportation? Which is the right move for you?

A MARTINEZ, HOST:

All right. At this moment, travelers can choose whether or not to wear a mask on most public transportation, but which is the right move for you? Here to tell us about the science of safer travel in the age of COVID is NPR health correspondent Maria Godoy. Maria, planes, trains, buses, rideshares - are the different types of transportation that much different from each other when it comes to the risk of getting infected?

MARIA GODOY, BYLINE: Well, yes, because it's all about the air we share with others and how it circulates. And that can be quite different depending on the mode of transportation.

MARTINEZ: All right. So which one should we start with?

GODOY: Airplanes.

MARTINEZ: Because we're all jammed together in that plane.

GODOY: Well, yeah, it's counterintuitive because you are in a small enclosed space. But every researcher I've spoken with agrees that the air filtration and ventilation on an airplane is really about the best it can be for an indoor environment. That cabin gets replenished with new air a lot. But there's a big caveat to that. Here's Dr. David Freedman. He's president-elect of the American Society of Tropical Medicine and Hygiene.

DAVID FREEDMAN: I think it's important to remember that this phenomenal ventilation is only phenomenal when the airplane is in the air with the wheels up, with both engines running fully.

GODOY: When you're in the crowded jetway, getting ready to board or even just sitting in your seat on the runway, that ventilation system isn't always running at full blast, and infectious aerosols can accumulate all around you. But when those systems are running, they're quite effective. Linsey Marr studies airborne virus transmission at Virginia Tech. She says airplanes filter the air every few minutes. But if someone sitting close to you is infectious...

LINSEY MARR: There's still a risk, though, of transmission with those immediately nearby, like, next to or the row in front or row behind.

GODOY: Or if you're standing in the aisle waiting for the bathroom. Marr says even if others aren't wearing masks, she's going to keep wearing an N95 on flights because those masks really do protect the wearer.

MARTINEZ: Me, too. All right. So after planes, what's next?

GODOY: Trains and buses. Marr says the data she's seen from the subway systems in New York City and San Francisco show they have good air ventilation. But if you are standing shoulder to shoulder with other riders, that ventilation alone won't be enough. And as for buses, the situation is worse. Jesse Capecelatro of the University of Michigan has researched how air flows on urban buses.

JESSE CAPECELATRO: What we found was if the windows are closed due to sort of the recirculation of the air in the bus, whatever someone breathes out, in about 45 seconds, everyone in the bus is breathing in a portion of that.

GODOY: Opening windows can make a big difference, but you can't always do that on buses. Capecelatro's modeling shows when everyone on a bus is wearing a mask, that dramatically reduces transmission risks. You know, I also spoke with Neil Siegel. He's a health policy researcher at the University of Maryland, and he says bad bus ventilation raises real equity concerns.

NEIL SIEGEL: Hispanic and Black people are more than twice as likely to take public transit than white people. And people with lower incomes are also disproportionately more likely to take public transit than people with higher incomes.

GODOY: Siegel says people with fewer options for safer travel are now facing increased risk.

MARTINEZ: One more thing really quick - a lot of people take rideshares. What should they know?

GODOY: Keep the windows open. If you're stuck in traffic, have the AC at full blast too to help clear the air.

MARTINEZ: That's NPR's Maria Godoy. Maria, thanks.

GODOY: My pleasure. Transcript provided by NPR, Copyright NPR.

Steve Inskeep is a host of NPR's Morning Edition, as well as NPR's morning news podcast Up First.
Maria Godoy is a senior science and health editor and correspondent with NPR News. Her reporting can be heard across NPR's news shows and podcasts. She is also one of the hosts of NPR's Life Kit.