The Petro Travel Center on Interstate 10 in Ontario, Calif., is one of scores across the country. At the front of the building are the things road trippers see when they stop for gas or snacks: a convenience store, restrooms and some dining options.

But for truckers, Petro is a haven.

An entrance opens to kiosks and services catering directly to those who work out of the cab of a big rig. There are showers, a driver’s lounge, a gym and a laundromat. A brightly lit game area features arcade machines and a pool table. Outside the stop there is a chapel in a trailer.

“For the next 34 hours I’m going to do laundry, catch up on some reading, take a shower — basically just like what anybody else would do if they were home for the weekend,” Bryan Tyson Galbreath, 41, of Corpus Christi, Texas, said. “I’m away from my house, but that truck is technically my house.”

Mr. Galbreath is one of at least 550,000 long-haul truck drivers in the United States, underpinning an industry that has been hailed as indispensable during the pandemic even while facing a severe shortage of drivers. That shortage has coincided with supply chain issues, adding pressure on drivers to reach their destinations on time.

The industry is also on the precipice of a huge change. The driver shortages are reshaping the work force, as the specter of self-driving trucks increasingly threatens to transform how the work is done. Self-driving trucks are being tested now and are viewed as the future for shipping all manner of goods across the country.

As trucking evolves, the patchwork of businesses across the United States that exist to support the industry is at risk of disappearing.

There are no figures on how many people work in the various professions that support the trucking industry, but it takes an army of truck washers, gas station cashiers and truck stop custodial staff to help drivers and their cargoes get from Point A to B.

Restrictions control how long they can drive, down to the minute, a reason Mr. Galbreath is spending 34 hours in the truck stop’s orbit.

Because of the dangers associated with having exhausted drivers at the wheel, various federal rules have taken effect since the 1930s. The current set of rules, enacted in 2013, are complicated. Depending on their companies’ operating hours, truckers are allowed to drive a maximum of 60 hours over seven days or 70 hours over eight days. So drivers on these schedules can set their time back to zero with so-called reset breaks. These 34-hour off-duty periods are often spent at truck stops.

“If you’re at a truck stop, you’re pretty much stuck there,” Mr. Galbreath said.

In the parking areas, the drivers nestle their trucks in tightly packed rows. Their cabs function as kitchens, bedrooms, living rooms and offices. At night, drivers can be seen through their windshields — eating dinner or reclining in their bunks, bathed in the light of a Nintendo Switch or FaceTime call home.

Small truck stops have just a few parking spots. By contrast, the Iowa 80 Truck stop, in Walcott, Iowa, bills itself as the largest truck stop in the world and has 900. Across the country, entire temporary cities form and disperse daily.

“Everybody has different stories,” Elaine Peralta said of the truckers that pass through her salon inside the TA Travel Center in Barstow, Calif. “There’s a lot of couples that are driving. There’s a lot of students driving. Young people are driving, and they do their school work, if they’re in college, on the truck. A lot of different ages.”

One common complaint among truckers is food quality. Except for the occasional diner, food truck or independent restaurant, fast food is the most readily available fare, with restaurants like Carl’s Jr., Wendy’s and Taco Bell dominating the truck stop market.

“I would like to see a little more variety and not just fast food,” said Angela Eudey, 42, of Bakersfield, Calif., who tries to shun it and stocks up on groceries before she hits the road. “I have a fridge, so I buy food each week,” she said. “Mostly fresh fruits, vegetables, yogurt, luncheon meat.”

“I try to be healthy,” the truck driver said.

Being healthy isn’t easy, though. With long hours behind the wheel and a lack of nourishing food options, truckers face a variety of challenges. Various studies have found that truckers have higher-than-usual rates of obesity, diabetes, back problems and depression and that long-haul drivers are more likely to smoke.

Another issue presented by truck stop food is the cost. As of 2021, the mean annual pay for a truck driver was $50,340 — down significantly from 1980, when the average pay was $110,000 after adjusting for inflation, according to one analysis. Pay can be especially low for new drivers, or independent contractors, as they can be on the hook for costs like training fees, maintenance and fuel.

“Everything is expensive,” said Anthony Johnson, who is 36 and based in Miami. “And I don’t get paid that much to keep buying food out in restaurants at all. And Uber Eats is worse. I’m constantly spending $30 for things that cost $9.”

At a stop in Barstow, Calif., truckers grilled tri-tip, burgers and sausages over a portable grill in the parking lot. “If you’re going to eat at the truck stop three meals a day, it’s going to cost you $75 to $100,” Bobby Parkman, 59, a truck driver from Center Rutland, Vt., said. “This is a lot better.”

Truckers aren’t always able to make it into truck stops or rest areas when they’re not working.

The United States has a huge shortage of truck parking spaces. According to the American Trucking Associations, over 98 percent of truck drivers have reported having difficulty finding safe parking. If no spots are available in designated areas, truckers have to improvise, spending their nights sleeping in potentially unsafe or illegal locations, like vacant lots or highway on-ramps.

For truckers, a good night’s sleep is essential. Driving a truck is incredibly dangerous, and tired drivers exacerbate the problem. In 2020, 4,842 large trucks were involved in fatal crashes — and 107,000 in crashes that resulted in injury. According to the Federal Motor Carrier Safety Administration, fatigue is a factor in around 13 percent of truck crashes.

“There’s been many a time I couldn’t find a spot,” said Mr. Galbreath, who has sometimes been forced to sleep on the side of the highway because of the lack of parking. “You have vehicles that are traveling down the highway at 65, 70 miles an hour.”

He continued: “You can feel them when they run by you, rocking the truck. You’re not going to get a good night’s rest doing that.”

Yet while truck drivers have adapted to increasing difficulties on the road, the problems ahead seem more transformational.

If driverless trucks are the future of America’s highways, the industry surrounding truckers is likely to head the way of other once essential, now forgotten support industries, like the businesses that once served gold rush towns, mining towns or Route 66 motorists.

“This is all I really want to do,” said Kevin Ransom, 46, who has been driving for 22 years. “I’ve tried welding. I’ve done carpenter work. I’ve done a variety of manual labor jobs, working in the plants, and I don’t care for it. So I don’t know what else I could do.”

He added that he was hopeful it would be another 20 years before automation would affect his job. “By that time,” he said, “I’ll be retired.”