A hit-and-run crash occurs about once every 18 minutes in Los Angeles, according to data analyzed by the NBC4 I-Team that illustrates the extent of a problem that has been called an "epidemic."

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The I-Team examined data reported to the California Highway Patrol on all hit-and-run cases in Los Angeles County for 2015. More than 28,000 reported hit-and-run crashes during that year occurred over a widespread area of the county at an alarming rate and 50 percent of all incidents in Los Angeles County are hit-and-run cases.

The national average is 11 percent, according to the American Automobile Association.

"The numbers are extremely high," said Los Angeles Police Detective Michael Kaden. "There is no rhyme or reason, that's why they call them accidents."

Most hit-and-run cases do not involve injuries, according to the data. They often involve a driver striking a parked vehicle, then leaving the scene.

But others leave families in grief and searching for answers. Frank Gillart is one of the faces behind those statistics. He was crossing a street in Los Angeles Feb. 20 when a sport utility vehicle driver ran him down and left him for dead.

"I couldn't believe that someone could just hit a person and keep going," said his sister, Olivia Holguin. "He was a father, he was an uncle, he was a person that was loved by many people."

There have been no arrests in the Gillart case, nor in the January hit-and-run death of 27-year-old Korina Campos. She parked her car on Boyle Avenue in Los Angeles and was struck by another driver as she was getting her 5-year-old daughter out of the car. Campos was killed and her daughter was injured in the crash caught on surveillance video.

In an effort to track down criminals in hit-and-run investigations, the Los Angeles City Council passed legislation that offers up to $50,000 in reward money for information to the arrest and conviction of anyone involved in a fatal hit-and-run crash.

"For whatever reason, there is this epidemic, and it seems to be growing," said Los Angeles City Councilman Mitch Englander, chair of the city's public safety committee.