SAN FRANCISCO — The double-length buses that snake through downtown San Francisco past the offices of Google and Facebook were empty. The teller at a Citibank in the city had seen three customers all morning, and the manager of a deserted sandwich shop a few blocks away decided to shut down for the rest of the week after selling only a handful of bagels.

The most ambitious experiment in America to stop the spread of the coronavirus — shelter-in-place orders for almost every resident — was underway for seven million people living around the San Francisco Bay on Tuesday. Another two million people were being asked to stay home under similar directives in the Sacramento and Monterey areas on Wednesday.

Silicon Valley was a sea of nearly empty office parking lots. Therapy and yoga classes continued — but online.

Across the notoriously congested Bay Area, traffic flowed like it was 3 a.m.

“Sunday has more people than this,” said Omar Tapea, who was closing down the sandwich shop in San Francisco for lack of customers.