LOS ANGELES — If you can navigate the maze of roads and freeways in this city and choose not to break a single traffic law, congratulations. You deserve a prize.

That prize could have been $20,000, in fact, if you had enrolled in the first L.A.’s Safest Driver contest this summer.

Deborra Sarei, 46, a resident of Downey, Calif., who takes the 105 to the 605 to Lakewood each morning to drop off her daughter at school, knew she was up to the two-month challenge. She faced off against 11,500 other entrants who reside in, or drive in and near, the city of Los Angeles. They participated by letting a mobile app spy on them behind the wheel to track phone distraction, speed, braking, acceleration and cornering.

With constant monitoring, Ms. Sarei quickly realized she’d need to recalibrate her driving habits. But driving “safer” sometimes got her into trouble on busy freeways.

“There were moments on the freeway where people would literally cut you off to go to the next lane,” Ms. Sarei said. “It was hard to prevent causing an accident because you had to brake and then accelerate to get out of the situation.”

Still, Ms. Sarei made sure to never creep past speed limits. To make up for the extra time spent on the road, she told her daughter to be ready to leave for school 10 minutes earlier than usual.

“When we were in the slow lane, we’d be going at a certain speed limit and people would be whizzing by us,” she said. “We started saying, ‘Well, you’re not going to be L.A.’s safest driver.’”

Ms. Sarei is now known as L.A.’s safest driver. The $20,000 purse and the bragging rights are all hers.

We Drive On

Last year, approximately 40,000 people in the U.S. died in car accidents and 4.5 million people were seriously injured, according to the National Safety Council.

In Los Angeles, the death toll from car accidents has gotten worse since the beginning of a major road safety initiative from Eric Garcetti, the mayor of Los Angeles, aimed at getting the number of deaths down to zero. Similar “Vision Zero” programs are beginning to see some positive results in many major American cities. In 2018, New York City recorded the lowest number of pedestrian deaths since 1910 — although pedestrians, along with bicyclists and motorcyclists, remain in serious danger.

Mayor Garcetti promoted L.A.’s Safest Driver competition — which is sponsored by USAA, a financial services company — as a way to support Vision Zero and “drive home the importance of keeping our minds and eyes on the road.” Similar safe driver competitions have been in held in Boston, Seattle and San Antonio.

There was also a military veteran division of the competition, as USAA serves military families. Javier Briones, 35, won that, and he attributed his success, in part, to not checking his phone while driving. He’d lock it away in the glove box. “That was my trick to get rid of the temptation,” he said.

As with Ms. Sarei, Mr. Briones spent most of his 40-mile round trip commute in the slow lane for the duration of the contest. (He takes the 105 from Santa Fe Springs to his job near the Los Angeles International Airport.) While he was at it, he incurred his fair share of other drivers’ wrath, especially while observing a drop in the speed limit from 70 m.p.h. to 55 m.p.h.

“I was like, ‘Hey, the $10,000 is more important than the honking, so I don’t care,’” he said.

Meet Big Passenger

The contest participants may have frustrated some L.A. motorists, but USAA is heralding it as a success. According to the company, phone distraction among all competitors improved by 26 percent, while the speeding scores of the drivers improved by 30 percent by the end of the contest.

In addition to the competition, USAA currently offers up to 20 percent discounts to certain policy owners who agree to let a separate mobile app track their driving.

Other large insurers, including State Farm, Geico, Progressive and Allstate, offer similar opt-in “usage-based” plans based on driving habits or distance traveled. One recent State Farm ad campaign depicts a woman in labor scolding her husband for speeding to the hospital in the family minivan. “Don’t mess with my discount!” she yells.

Cambridge Mobile Telematics, the company that built the app for the L.A.’s Safest Driver competition, stands to gain as much as anyone from the adoption of these plans. In December, the start-up raised a half billion-dollars from Japanese conglomerate SoftBank to expand its usage-based Drive Well program.

Hari Balakrishnan, a co-founder, said the program, unlike many traditional insurance plans that use markers such as age or ZIP code to determine premiums, allows “for rate-setting based largely on factors that drivers can control.” The Drive Well app, which Mr. Balakrishnan described as a “social gamification of driving,” is used by more than 10 U.S.-based insurers already. That includes State Farm, Liberty Mutual, Safeco and Nationwide, he said.

For now, USAA’s discount program is only meant to encourage safety, said Randy Termeer, that company’s general manager of auto insurance. Premiums won’t increase because of bad driving. Some competing programs, such as Progressive’s Snapshot, do reserve the right to hike rates based on driver behavior. But in California, insurance rating rules currently prohibit companies from offering policies based on driving habits. For now, at least. The state’s top insurance regulator is reportedly eager to roll back those restrictions.

Jennifer King, the director of consumer privacy at the Stanford Law School Center for Internet and Society, said it’s not hard to imagine usage-based technology one day becoming a standard method for setting most insurance premiums.

If this eventually does come to pass, drivers might have to worry that even minor transgressions such as pulling in too quickly to snag a parking spot or rerouting Google Maps could potentially raise their rates.

“There’s been a market for at least a decade of installing devices in teenagers’ cars to track what they do to force them to drive more safely,” Ms. King said. “Why wouldn’t insurance companies want to do that for everybody?”

Now that the competition is over and nothing is monitoring her driving, Ms. Sarei has returned to some of her old habits, she said, including accelerating onto the freeway and going with the flow of traffic.

It’s something of a relief. “I don’t have the app looking over my shoulder,” she said.