By David Harrison | Photographs by Caitlin O'Hara for The Wall Street Journal

PHOENIX -- The light rail glides through downtown, disgorging commuters with a jangle of bells every 12 minutes. Just a few blocks away, Interstate 10 is backed up for miles.

"It's so difficult to drive here every single morning, so I park my car at Mesa and I take the light rail," said Jackie Rios, a freshman at Arizona State University's downtown campus as she waited to board a train on her way home to suburban Chandler.

Like Ms. Rios, many residents here and across the country are increasingly ditching their cars.

Around the country, the American love affair with driving is cooling in ways that are changing how cities look and feel. Over the past three years, the average number of miles driven per person has hovered around 9,800 miles a year, roughly 2% fewer than at the 2004 peak. Driving is down in states with urban centers like California and New York and in some rural states such as Wyoming and Vermont.

Driving is even down here in Phoenix, the sprawling, fast-growing desert metropolis built around the automobile. Per capita driving in Maricopa County, which includes the city, has dropped almost 7% since 2006, according to data from the state's transportation department. Statewide, driving is down 11%.

Among the reasons for the national decline are migration to dense urban areas; young adults' preference to live close to their jobs or to use alternate modes of transportation; more online working, shopping and streaming; and a growing population of retirees who don't commute to jobs anymore.

For decades, the country's driving pattern moved in sync with the economy. People drove more when times were good. They cut back when recessions cost them their jobs.

Now, however, we're driving less even though the economy has been expanding for more than a decade.

"In the midst of a fairly substantial economic recovery between 2009 and 2017, we're seeing a decline in person trip-making, which suggests that something pretty fundamental is going on here," said Brian Taylor, a professor of urban planning at the University of California Los Angeles.

Gains in miles driven per person started to slow in the mid-1990s, despite strong economic growth. During the expansion of the mid-2000s, Americans cut back on driving, perhaps due to rising gas prices at the time. After a modest postrecession rebound between 2014 and 2016, the number of miles we put on our vehicles each year has stagnated below the 2004 level.

The automobile remains the predominant mode of transportation. Slightly more than three-quarters of American workers drive to work. Nationally, the total number of miles driven continues to rise as the population grows. Ride-hailing services such as Uber or Lyft have exploded in popularity. And annual auto sales have hit records recently.

Still, a raft of data suggests Americans are changing how they move around.

Younger people are delaying getting their driver's licenses and using them less than their predecessors. Drivers aged 16 to 19 drove 24% fewer miles in 2017 than did people of the same age in 2001, according to U.S. Transportation Department surveys. Those aged 20 to 34 drove 22% less.

People also aren't leaving home as much. In 2017, households took fewer commute trips on average than at any point since 1990, according to DOT surveys. The number of trips for shopping, socializing or recreational activities has also declined.

The share of workers who work from home every day has risen to 5.3% in 2018 from 4.3% in 2010, according to the U.S. census. Many more workers -- roughly 15% -- work from home for a full day once in a while, according to the Labor Department.

Anne Folger, senior director of physician and provider recruitment for Banner Health, a large Phoenix-based health-care provider, said working from home saves her almost three hours of commuting every day and has significantly reduced the amount she drives. She also shops online, further reducing her time in a car.

"When we're not working we're exercising, we're doing family events, we're visiting with people," she said. "It's a much more enriched lifestyle when you have that convenience because you're not going to run errands to find that one item you have to search for at the hardware store."

Roughly 2,200 of Banner Health's 51,000 employees telecommute every day while others work from home occasionally. The company -- Arizona's largest private employer -- also moved its corporate headquarters to a downtown location close to public transit to make commuting easier. Those moves help attract and retain talent, said Naomi Cramer, the company's head of human resources.

"We're also looking at a four-day workweek and other things like that," she said. "People are raising their hand quite a bit."

Forecasts suggest the trend could last. The Energy Department anticipates overall driving will grow at a modest 0.6% annual pace. That is down from the 1.5% growth rate the department projected in 2009.

Evolving travel patterns have prodded urban planners to take steps that would have been unthinkable just a few years ago. They are reducing the number of lanes on city streets, intentionally slowing down traffic and making room for bicycles, pedestrians and public transit. They are eliminating parking requirements for new construction. And they are welcoming the proliferation of shared bicycle and scooter services.

In Phoenix, planners are now focusing much of their energy on people who don't drive. Offering alternative modes of transportation will help the city keep growing without becoming paralyzed by congestion, said Mario Paniagua, Phoenix's deputy city manager.

Despite adding about 100 new residents a day, city officials have cut traffic lanes on several thoroughfares to make room for bicycle lanes. The regional light-rail system opened in 2008 with 20 miles and has since added eight with plans for another 42 by 2050. Planners also want to expand the bus system.

Getting around by bicycle is increasingly popular, despite the summer heat. The city's bike-share program doubled its ridership over two years.

"Phoenix was made for the car, and it's going to take a long time to change that," said Annie Eldon, a local bicycling advocate.

Ms. Eldon put off buying a car for several years after moving to town. Even now, she uses it sparingly, preferring to bike.

"I have gone days without using my car," she said. "I think it's becoming more common."

Some of the changes haven't been as well- received. On South Central Avenue, a strip of tire shops and discount plazas, businesses are wary of a planned light-rail extension that will cut the number of car lanes from four to two.

Fewer lanes will reduce traffic flow and hurt the businesses that rely on passing cars, said Celia Contreras, owner of Tony's Window Tinting.

She's seen the new condominiums and apartments with ground-floor retail that have risen along the existing light-rail line and worries the same could happen in her neighborhood. Those ground-floor businesses cater to pedestrians rather than drivers, she said. "They don't want a business like mine."

Earlier this year, activists opposing the extension succeeded in putting a referendum on the ballot that would have canceled all future light-rail construction and redirected the money to road and bus projects.

At stake in the August special election was an existential question: Would cars continue to hold undisputed sway in Phoenix?

In the end, almost two-thirds of voters supported building more light rail.

Soo Oh contributed to this article.

Write to David Harrison at david.harrison@wsj.com