Dec. 15, 2020 6:00 am ET Transit officials in New York are teaming up with the Department of Homeland Security and Massachusetts Institute of Technology to study how to reduce the spread of the new coronavirus on buses and trains. If—and how much—the virus spreads on mass transit is a stubborn question. Ridership is down in cities around the world largely due to people working from home and businesses closing, but also because of fear of contracting the virus. Studies and reports this year have drawn conflicting conclusions about the extent to which the virus spreads on mass transit. Some of the studies have been conducted by economists and transit specialists who don’t have expertise in the spread of viruses and other pathogens.