Mass transit systems around the world have taken sweeping steps to curb the spread of the coronavirus, including shutting down some subways overnight and testing powerful ultraviolet lamps to disinfect seats, poles and floors.

But experts say those steps solve only part of the problem because the virus is more often spread through the air.

Transit officials are studying more advanced cleaning methods that might someday automatically disinfect transit systems around the clock.

The Moscow Metro and a public bus company in Shanghai have experimented with germ-killing ultraviolet light.

Agencies in Hungary and the Czech Republic have tried using ozone gas as a disinfectant.