Five months after the coronavirus outbreak engulfed New York City, riders are still staying away from public transportation in enormous numbers, often because they are concerned that sharing enclosed places with strangers is simply too dangerous.

But the picture emerging in major cities across the world suggests that public transportation may not be as risky as nervous New Yorkers believe.

In countries where the pandemic has ebbed, ridership has rebounded in far greater numbers than in New York City — yet there have been no notable superspreader events linked to mass transit, according to a survey of transportation agencies conducted by The New York Times.

Those findings could be evidence that subways, commuter railways and buses may not be a significant source of transmission, as long as riders wear masks and train cars or buses never become as intensely crowded as they did in pre-pandemic rush hours.

If the risks of mass transit can be addressed, that could have sweeping implications for many large US cities, particularly New York, where one of the biggest challenges in a recovery will be coaxing riders back onto subways, buses and suburban trains — a vast system that is the backbone of the region’s economy.

When the city shut down in March, over 90 per cent of the subway’s 5.5 million weekday riders abandoned the system. Even now, as the city has largely contained the virus and reopened some businesses, ridership is still just 20 per cent of pre-pandemic levels.

“What we are seeing in other cities makes me optimistic,” said Toph Allen, an epidemiologist who co-wrote a report on coronavirus transmission and public transportation with the Tri-State Transportation Campaign, a transit advocacy group. “If you know that you have a transit system that is functioning in an area where there are no major outbreaks, you know transit can be safe.”

In Paris, public health authorities conducting contact tracing found that none of the 386 infection clusters identified between early May and mid-July were linked to the city’s public transportation.

A study of coronavirus clusters in April and May in Austria did not tie any to public transit. And in Tokyo, where public health authorities have aggressively traced virus clusters, none have been linked to the city’s famously crowded rail lines.

But public health experts warn that the evidence so far should be considered with caution. Ridership in other major cities is still well below pre-pandemic levels, tracing clusters directly to public transit is difficult, the quality of ventilation systems used to filter air varies, and the level of threat depends to a high degree on how well a city has reduced its overall infection rate.

“There are so many other factors that go into levels of risk and how you assess risk,” said Dr Michael Reid, an assistant professor at the University of California, San Francisco School of Medicine and a contact-tracing expert. “They are not equal comparisons.”

In fact, state and city officials have been unable to determine whether mass transit in New York contributed to the surge in March and April that devastated the city, killing more than 20,000 people.

The outbreak has exacted an especially devastating toll on transit workers. To date, over 4,000 have tested positive and 131 workers have died from the virus — nearly 90 per cent of whom worked for the division that runs the city’s subways and buses.

For much of that time, riders were not required to wear masks, and the infection rate in the city was much higher than it is today, likely making public transportation a riskier venue.

Still, some public health experts believe the experiences of other cities offer a blueprint for how to minimise the potential for transmission on public transit systems.

Among the range of urban activities, the experts say, riding the subway is probably riskier than walking outdoors but safer than indoor dining.

The low infection rates on some public transportation systems can be attributed, in part, to measures transit agencies have adopted, including mandating face masks; disinfecting trains and buses; and ramping up service and asking businesses to stagger work hours to reduce rush-hour crowding.

New York officials are trying to balance two goals: drawing as many riders back as possible while also avoiding sardine-can crowding at rush hour. They have appealed to business leaders to have employees start at different hours, though the pressure on the system has eased notably since the shift toward working from home is expected to last for months, if not longer.

Even as public transit ridership has rebounded in cities such as Paris, there have been no major outbreaks linked to mass transportation.

“Each of these things layers one on top of the other to make things safer,” said Dr Don Milton, an environmental health researcher and aerosol transmission expert at the University of Maryland.

The nature of how people use public transit also may help explain why potential exposure levels might not be as high as some riders believe.

People tend to stay on trains or buses for relatively short amounts of time, compared with a day’s work in an office or an outing to a bar to see friends. Riders tend not to talk on the train, reducing the amount of aerosols they release. In many cities, lockdown orders and new work-from-home norms have minimised crowds on trains, making it easier to keep some social distance.

“We were pleasantly surprised that Berliners accepted it so quickly,” said Jannes Schwentu, a spokesman for the Berliner Verkehrsbetriebe, which operates Berlin’s subway and buses, referring to mask compliance.

In New York, transit officials say that a recent observational study of over 220,000 riders found that over 90 per cent were wearing masks. The transit agency has handed out free masks to passengers.

Though some veteran riders might be surprised, the subway system also benefits from a robust ventilation system that is effective at removing viral particles from the air.

In New York’s subway trains, transit officials say, the filtered air that circulates through a car is replaced with fresh air at least 18 times an hour. That is a much higher than the recommended air-exchange rates in restaurants, where recycled air is replaced eight to 12 times per hour, or in offices, where it is replaced six to eight times an hour.

This sharply reduces the chances of a superspreader event on trains, as long as they do not become overly crowded, said Linsey Marr, an expert on the airborne transmission of viruses at Virginia Tech.

But once too many people pack a train, the ability to provide proper ventilation to prevent the spread of viral aerosols diminishes significantly. When riders are standing shoulder to shoulder, any viral particles a sick passenger exhales could be readily inhaled by another passenger — which is possible even if both are wearing masks.

In Beijing, subway ridership has risen to 59 per cent of pre-pandemic levels; in Tokyo, Metro ridership has increased to 63 per cent; in Berlin, ridership on buses and subways is between 60 to 70 per cent of normal rates; and in Paris, ridership on the Metro has returned to 45 per cent of usual levels.

“I am more vigilant in the Metro and careful not touching the bar or sitting on seats,” said Alain Raphael, 28, an engineer in a tech company in Paris. “I am less confident in bars, cafes and restaurants than riding the Metro.”

New York Times News Service