In a study released this month, a team of researchers at New York University found that fears about virus transmissions in public transportation systems could be exaggerated.

While acknowledging that “transportation of any type is clearly associated with the spread of disease from one geographic region to another,” researchers from NYU’s Robert F. Wagner School of Public Service and the Rudin Center for Transportation found that high public transportation ridership didn’t necessarily translate to a greater number of deaths from seasonal flu or pneumonia.

For their analysis, the team looked at a decade’s worth of data from the Centers for Disease Control and Prevention of deaths linked to flu and pneumonia in 121 cities and compared it with data on public transportation ridership from the U.S. Census Bureau.

The goal was not to determine whether people who took public transportation were more likely to get sick than those who didn’t, but rather, whether infections were more widespread in cities where more people used public transportation more heavily.

Researchers found no concrete link.

“The evidence is mixed about whether exposure to public transit is any more dangerous than interactions that occur in schools, workplaces, businesses, religious gatherings, sporting events, and neighborhoods and whether the use of public transit increases the rate of community transmission of influenza, even among those who do not themselves use transit,” the study’s authors concluded.

New York City, for example, which has one of the highest rates of public transportation usage, recorded among the lowest number of deaths from influenza and pneumonia, NYU’s analysis found.

The team launched its study before the beginning of the coronavirus pandemic, but it says because the coronavirus spreads in ways similar to the seasonal flu, their findings could apply to the current health emergency. Their conclusions also mirror other studies that examined the relationship between public transportation and virus transmission.

Researchers acknowledged their findings go against what many have come to believe about the risks of riding public transportation. For example, even before stay-at-home orders were issued in New York, ridership on its subways had dropped 50 percent as of March 15, when compared with the same day in 2019.

Sherry Glied, dean of NYU’s Robert F. Wagner Graduate School of Public Service and a member of the research team, said people are naturally concerned about public transportation because it’s a setting that brings strangers together in a confined space. But subways might be unique in that while they are places where strangers come together, those encounters often are brief. People don’t tend to speak with each other and do their best to stay separated. That’s unlike other settings such as bars and restaurants where there is more interaction, Glied said.

Subway cars also have surprisingly good ventilation systems, researchers found. In New York, officials at the Metropolitan Transportation Authority said air in subway cars is filtered and replaced with fresh air at least 18 times an hour. In D.C., officials with the Washington Metropolitan Area Transit Authority said air is replaced in subway cars roughly 20 times an hour.

“Cities with the highest use of public transportation did not have the highest rates of deaths; if anything just the opposite,” William A. Petri Jr., a professor of internal medicine and associate director of microbiology at the University of Virginia Medical School, said via email. “The authors are careful to point out the limitations of the analysis, but it really argues against conventional wisdom, and suggests that with proper safeguards of masking and social distancing that public transportation could be used safely.”

However, Donald Milton, an expert on aerosol transmission, who is a professor of environmental health at the University of Maryland School of Public Health, questioned the research.

“The value of this ecological analysis is not clear to me,” he said in an email. “The finding, after controlling for population density, that having a lot of people on public transportation isn’t associated with greater rate of people dying of influenza and pneumonia (many of whom are elderly and may not be working and riding public transportation at times when the trains and buses are congested) doesn’t help me understand the risk of public transportation.”

Glied said with the current pandemic it can be hard for people to wrap their heads around the idea that personal, intimate relationships may put them more at risk than quick encounters with strangers on a subway car.

Melissa Perry, an epidemiologist who chairs the Department of Environmental and Occupational Health at George Washington University’s Milken Institute School of Public Health, said one of the strengths of the study was the large data set it used to draw its conclusions.

“That’s very powerful,” she said. “It’s a bigger picture, rather than a snapshot.”

Perry said if there is one disconnect, it’s that the data only allowed researchers to look at deaths, not actual infections. Since a variety of factors can impact the severity of an infection, deaths offer an imprecise proxy for infections, she said. (The researchers noted that limitation in their study.)

Even so, Perry noted that other studies examining the connection between public transportation and disease transmission have drawn similar conclusions.

Still, she emphasized the importance of following CDC recommendations when riding public transportation, such as wearing masks, using hand sanitizer or washing hands before and after arriving at a destination, and riding at low-traffic times to avoid crowding.

Said Perry: “The more routine and commonplace these [behaviors] become, the more impact we can have on reducing transmission and slowing the epidemic.”