The agency says about half of its drivers are out on some form of COVID-19 related leave. Only six of Muni's 2,000-plus operators have tested positive for the coronavirus so far, but that's forced employees who came into contact with them to self-quarantine.

Some workers are off because they are in vulnerable groups themselves. Others are caring for vulnerable or sick family members or children who are home from school.

In response, the agency has shut down its light rail network, mothballed streetcars and cable cars and, most recently, suspended 80% of its bus lines and refocused the remaining service on routes that get people to major medical facilities and commercial hubs.

But Tumlin sees much more work ahead. One priority task: reducing crowding on the 17 core bus routes the agency is still running. That's necessary so that riders can maintain the required minimum six feet of physical distance from other passengers.

To do that, Tumlin says Muni is actively discouraging "non-essential travelers" from riding, emphasizing that the remaining service should be reserved for those whose travel is truly necessary: hospital workers, first responders, those on their way to other essential work and people headed to medical appointments or other needed errands, such as grocery shopping.

He says a wide range of people are still getting on buses when they don’t have to.

"There are a lot of San Franciscans who just decide, ‘It’s a nice day, so I’m going to take Muni out to the beach,'" Tumlin said in an interview earlier this week.