DETROIT — Paris Banks sprayed the seat with Lysol before sliding into the last row on the right. Rochell Brown put out her cigarette, tucked herself behind the steering wheel and slapped the doors shut.

It was 8:37 a.m., and the No. 17 bus began chugging westward across Detroit.

On stepped the fast-food worker who makes chicken shawarma that’s delivered to doorsteps, the janitor who cleans grocery stores, the warehouse worker pulling together Amazon orders.COLLEGES AT A LOSS The pandemic has already cost universities millions of dollars, now they’re worried about losing students, too.

By 9:15, every available row on the bus was occupied. Strangers sat shoulder-to-shoulder. The city might be spread across 139 square miles, but one morning last week there was no way to socially distance aboard this 40-foot-long New Flyer bus. Passengers were anxious and annoyed. Resigned, too.

“I don’t like it, but it’s something you have to do,” Valerie Brown, 21, the fast-food worker, said through a blue mask. She was on her way to work at a local Middle Eastern fast-food chain.

This hardscrabble city, where nearly 80 percent of residents are black, has become a national hot spot with more than 7,000 infections and more than 400 deaths. One reason for the rapid spread, experts say, is that the city has a large working-class population that does not have the luxury of living in isolation. Their jobs cannot be performed from a laptop in a living room. They do not have vehicles to safely get them to the grocery store.

And so they end up on a bus. Just like the No. 17 — a reluctant yet essential gathering place, and also a potential accelerant for a pandemic that has engulfed Detroit. It is a rolling symbol of the disparity in how this virus is affecting Americans.

After the city’s roughly 550 drivers walked off the job for a day in mid-March because of safety concerns, city officials put in effect new measures. Riders had to enter through the back doors. Drivers would be offered gloves and masks. Buses would be cleaned more frequently.

Later, Mayor Mike Duggan said all of the city’s front-line employees, including bus drivers, would get $800 a month in hazard pay. He also announced that masks would be made available to riders on all buses.

But on the first day of the mask initiative last week, there were no masks on board the No. 17 bus Rochell Brown was driving.

A manager told her that riders were not required to wear them.

Ms. Brown, 49, shook her head and thought about a colleague who died this month from complications of Covid-19, the disease caused by the coronavirus. “It should be mandatory,” she said of the masks.

She saw herself at risk of a similar fate. She had a heart attack two years ago and has hypertension. The night before this ride, her doctor suggested she take time off for her safety.

Yet here she was, on a sun-soaked, mild spring morning, performing an “essential” duty for $19.13 an hour, but without, she felt, the praise and appreciation that police officers and emergency medical workers received. No one was peering out of a window clapping for her. Her bus was not even equipped with masks.

The 17 line cuts a roughly 25-mile path across Eight Mile Road, the infamous dividing line between black Detroit and the white suburbs.

The route tells the story of these bizarre times. It traces streets devoid of traffic, winds through the completely empty parking lot of a temporarily shuttered mall and dips into the bustling parking lot of a grocery store, one of the few businesses that can still attract big crowds.

That’s where Demetrius Jordan, 37, hops off to work his job as a janitor. First order of business at work: wash his hands. The trip was a necessary risk for Mr. Jordan, who said he worried most about the people whose only respite from the elements was a seat on the bus. 

“My concern is about the homeless people on the bus,” he said, adding that they were endangering themselves and others. “Are they being checked out?”

A notice on the Detroit Department of Transportation website asks “that customers limit nonessential bus travel.”

Drivers and passengers going to work say that is not happening. This trip on the No. 17 attracted riders headed to the store, to visit friends and family, and at least one homeless man.

Riders should be required to present proof that they are performing essential duties, Ms. Brown said.

“I would appreciate that — show some paperwork why you’re out here, what I’m risking my life for,” she said. “To me, too many people don’t care.”

A rider stepping off another No. 17 bus vented her frustration.

“I’m an essential worker,” she yelled. “I have to get out here and get the bus, but I’m tired of getting on this bus with people that want to visit other people because they ain’t working and they’re at home and they’re bored.”

Ms. Brown, the fast-food worker, boarded at the corner of East Eight Mile and Kelly Roads shortly before 9 a.m. to a bus that was still relatively empty. She sat at a window on the left. But within 20 minutes, a man sidled up right next to her.Sign up to receive an email when we publish a new story about thecoronavirus outbreak.Sign Up

“It was kind of irritating because there was a lot of space,” she said later. “I was like, why do you want to sit right next to someone when there are so many seats?”

With roughly the front third of the bus blocked off to protect the driver, passengers that morning were left with 29 seats to choose from. At peak ridership, there were 21 people on board at a single time.

Despite a statewide stay-at-home order, the buses are often packed, Ms. Brown said. If a bus is too crowded, she will sometimes wait for the next one. She does not like taking chances.

She lives with her mother, who is 42 and recently battled pneumonia. Ms. Brown does not want to bring the coronavirus home to her, or to her father and three siblings who also live in the four-bedroom house in the neighboring town of Eastpointe.

“I’m risking bringing it home,” said Ms. Brown, who rides the bus seven days a week. “And I work at a restaurant. It’s a high risk for it, and you can’t do anything about it really if your job is still open.”

The bus made it to the end of the line in a brisk hour and 38 minutes. It headed back the other direction, and as more and more passengers piled on — most wearing masks — tensions rose.

When a rider tried to take a seat next to a young man with an American flag bandanna tied around his neck, the young man stopped him and pointed him to another seat. He then pulled the bandanna over his nose and mouth and tightened it.

An older woman carrying two shopping bags wedged herself into a seat in front of two riders. One of those riders recoiled, wondering why the woman had come so close. “Excuse me,” she said, “the six-feet distance.”

The older woman pointed across the aisle to where she had been sitting and said the woman behind her had been coughing. She wanted no part of that. The woman who had coughed was close enough to hear, and she mumbled a few choice words beneath her yellow mask.

Ms. Banks, who sprays her seat with Lysol before sitting, wondered whether the reduced service contributed to the packed buses. During the week, the buses are running on the Saturday schedule, meaning they come less frequently.

“I take my own precaution by disinfecting; I still don’t think it’s safe,” she said.

She was “a little scared” about riding the bus, she said, and sometimes asked her co-workers for a ride. Ms. Banks, 27, said she worried that if she became infected, she would pass on the virus to others because her job with the National Guard often has her around a lot of people.

The crowds do not faze all passengers.

John Porter spread out on the back seat in black sweatpants and an unzipped brown jacket, his mustachioed face uncovered. He was headed home after his wife took the car to work.

“I believe in the Lord,” Mr. Porter, 63, said. “If it’s going to happen, it’s going to happen.”

A.J. Harris, 24, wore a mask but said he was not concerned about riding the bus. His attitude seemed more of resignation than bravado.

“These buses have been dirty long before the coronavirus was going on,” said Mr. Harris, on his way to work at an Amazon warehouse. “You got on the bus every day with people having H.I.V. and bedbugs, all types of diseases. It’s just another dirty bus coming along.”

Ms. Brown, the driver, does what she can to manage the crowds.

She does not allow anyone to stand — most other drivers do, so passengers tend to gripe when she tells them to sit. She will pass up stops when her bus is full, though she is loath to do that because she knows that some people need to get to work on time.

As she zoomed past a couple of stops, waiting riders threw their arms in the air. One person threw a plastic shopping bag at the bus.

Ms. Brown sees the disgruntled reactions and hears the snide comments coming from the back of the bus. On her way back to the beginning of the line, a man cursed her because she would not let him off between stops.

She arrived back to the first stop — on a wide road between a hospital and brick bungalows — at 11:57 a.m. Three hours and 20 minutes, and she had had enough.

Shortly after she stepped off the bus, a couple of passengers came asking for masks. Another driver who did not have masks on his bus would not let them get on without one. She did not have any, she told them, and they vented their frustration.

“This is stressful,” Ms. Brown said, and right there she decided it was best she followed her doctor’s advice. She was taking a two-week medical break.

This week, things were getting worse for riders, Valerie Brown, the fast-food worker, said in a text message. Officials had put signs on some seats, asking passengers to leave them vacant, but the message was being ignored, she wrote. It was standing room only on one ride, she said, yet the driver continued to pick up riders.

Ms. Brown texted two face-slapping emojis. “It’s never going to get better here.”