“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.