They could suggest steps to reduce crowds like limiting people’s use of subways and buses to travel that is absolutely essential, like going to and from work, or changing train schedules to discourage travel during peak hours.

Even in a severe pandemic, the C.D.C. recommends that essential services like public transit continue to operate so that health care workers and other emergency responders can get to work.

It is more likely that city officials would try to reduce the use of public transportation by asking businesses to stagger working hours, as happened during the 1918 influenza pandemic, or letting their employees work from home.

In other cities around the world, some officials have taken more stringent steps to contain the virus’s spread by effectively quarantining entire cities.

In China, government officials suspended public transit to and from Wuhan, the epicenter of the coronavirus outbreak. In Italy, officials have set up roadblocks in at least 11 towns in the northern part of the country, which is among the most infected regions, to prevent people from leaving or entering the area.

“What we saw in Wuhan and elsewhere is really a last resort,” Dr. Morse said. “At that point there’s little else they can do to contain it.”