SAN FRANCISCO (NYTIMES) - 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 under way for seven million people living around the San Francisco Bay on Tuesday (March 17).

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 3am.

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

Seven counties on Monday (March 16) ordered that people stay inside - and leave their homes only to "obtain or perform vital services".

Health officers described it as a radical but necessary step to save lives. With more than 200 confirmed infections and five deaths attributed to the coronavirus in Silicon Valley alone, officials say what has been a major hot spot for the disease is worsening quickly.

"This is moving so fast," Ms Sara Cody, the health officer for Santa Clara County, said on Monday when announcing the measures. "We needed to take very, very swift action."

As other parts of the country contemplate similar measures, the shelter-in-place order in the Bay Area is testing the willingness of a go-it-alone society to curb personal behaviour for the greater good of the community, especially older people and those vulnerable to severe disease because of medical conditions.

It is also an effort that does not come without huge costs for the tens thousands of people whose jobs in the Bay Area rely on people patronising restaurants, taking taxis, staying in hotels or appreciating art and music.

At the heart of the order is the difference between essential and nonessential, a distinction that seemed open to interpretation.

A store selling house paints in Santa Clara, in Silicon Valley, was open, but a nearby shoe store was closed. In Oakland on Tuesday a few joggers with their dogs ran along the banks of Lake Merritt.

In San Francisco, construction workers installed partition walls on skyscrapers. Starbucks baristas stood ready to serve the rare customer. Traffic police officers pasted parking tickets onto windshields. Late on Tuesday, City Hall reversed an earlier decision by declaring that marijuana dispensaries were considered essential and could remain open.

Some people who went to work said, essential or non-essential, they would not survive without the income.

In the shadow of San Francisco's tallest building, Mr Ricardo Valencia trimmed back the branches of sidewalk trees.

"The government says stay at home," Mr Valencia said. "But who is going to pay the rent?"

Mr Juan Carrillo, the owner of a taco truck who was fuelling in Richmond, across the Bay from San Francisco, said he would stay open until someone ordered him to stop.

"This is what I do for a living. If we close down for two, three weeks, it's going to be a problem," Mr Carrillo said. His employees, he said, have enough to survive "day by day".

And across the Bay Area, there were those who had nowhere else to go: More than 30,000 homeless people live in the counties affected by the orders.

It was left up to the counties and cities to decide what was essential and in a modern society, it turns out, that can be a lot.

Mr Mike Callagy, the county manager for San Mateo, one of the jurisdictions carrying out the order, went down a partial list of what was staying open: child protective services, the sheriff's offices, the jails, sewer maintenance crews and homeless services.

Healthcare outlets, pharmacies, gas stations and grocery stores are allowed to remain open and receive customers, according to guidance by the city of San Francisco. Also exempted: farmers' markets, car repair shops, hardware stores, dry cleaners and companies that provide payroll or security.

The emptying of cities did not come all at once. As the coronavirus spread into Silicon Valley, a flurry of memos from technology companies allowed their employees to work from home.

"Every morning there have been fewer people than the day before," said Dr Andrew Whyman, a retired psychiatrist who was returning from a pharmacy on Tuesday morning clutching a pack of toilet paper, the rare commodity that his wife, Barbara, had procured by reserving it early by phone.

"I think we are near rock bottom," Dr Whyman said, scanning the scant foot traffic on the sidewalk. "This is the middle of the week in San Francisco!"

On Monday evening, hours after the shelter-in-place order was announced, workers bid farewell to colleagues, often not knowing when or if they would see one another again.

A group of seven bartenders, baristas and cooks congregated outside The Hatch, a bar in downtown Oakland, commiserating after their last shifts for at least three weeks. Hours earlier, they were all told that they were out of jobs indefinitely and to file for unemployment.

"If people are afraid to go out, then we don't have a job," said Mr Garrett Hallstrom, a sous chef at Beauty's Bagel Shop in Oakland.

There were mixed emotions in the group: The forced time at home was a chance to catch up on long-delayed projects and hobbies, write short stories, play Dungeons & Dragons - to name a few of the ideas mentioned.

But there was also a fear of loneliness. Ms Jess Rankin, the lead barista at Beauty's Bagel Shop, said there were already plans afoot to stay in touch.

Beauty's two owners told the staff of roughly 50 people that they could take home perishable food and toilet paper on Monday, and that the establishment planned to host dinners for staff at the restaurant each Monday and Thursday while the shelter-in-place orders remained in effect.

"I can't just stay in my house because somebody tells me that a disease might impact me," Mr Hallstrom said. "I don't have people in my life that I'm going to infect if I get this disease."

Ms Rankin said she planned to mostly stay in, but she, too, would likely gather with friends and family in small groups during the lockdown.

"Three weeks is a long time," she said.

Others said they would try their best to abide by the orders. Ms Emily Straley, a civil engineer, said she was trying to isolate herself as much as possible to reduce her risk of contracting the virus or spreading it.

"I would feel horrible if I found out I somehow spread it to someone else," she said.

But as the shelter-in-place orders came into effect, Ms Straley said she wondered how they would be enforced.

"Having the police enforce something so vague makes me really nervous," she said. "Are they going to tell people to go home? Are they arresting people or writing tickets? I'm really confused about that."

Mr Sam Liccardo, the mayor of San Jose, the largest city affected by the shelter-in-place orders, said cities were still scrambling to interpret what kind of gatherings would be allowed and which would be shut down.

"There would be no reason to enforce the order except for some egregious green beer St Patrick's Day party that 2,000 of my Irish family members might put on," Mr Liccardo said.

"It's a mandate of common sense," he said. "We need everyone to recognise that it's in our collective best interest to stay home for all but the most essential of activities."