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.