In the last five years, 57 bikers and pedestrians have been killed in San Diego County by drivers who left the scene without stopping to help.

The numbers come from the San Diego County Medical Examiner’s Office, which works with law enforcement agencies to investigate how people died.

The carnage and accident scenes often yield few clues. Sometimes a passing motorist, or pedestrian, saw the crash and phoned police. Other times police relied on debris left at the scene: a broken side-view mirror, paint chips, an abandoned hubcap.

READ MORE: The Year of the Deadly Hit-and-Run

About 40 percent of these hit-and-runs happened in the city of San Diego.

And from 2008 to 2012, the most recent data the California Highway Patrol makes available, nearly 6,900 other victims were injured countywide in hit-and-run incidents.

NBC 7 called a recent rise in hit-and-runs an epidemic. And indeed, 11 pedestrians or bicyclists have been hit and killed this year by drivers who fled the scene – already one more death than the average for five previous years, which is 10. And it’s only June.

While those numbers may be too few to represent a large-scale pattern, national numbers have trended upward in recent years.

According to the National Highway Traffic Safety Administration, hit-and-run fatalities rose nationally between 2009 and 2011, the most recent data the agency makes available.

Within those stats, Southern California stands out. In Los Angeles – which has been called the nation’s hit-and-run capital – drivers fled the scene in nearly half of all collisions in 2009.

Due to the recent uptick locally, and because pedestrian deaths illustrate the most unsettling, apparently random aspects of the crime, I decided to zero in on just the number of people who were killed while walking or riding bikes.

The death tally would be higher if it included the people riding motorcycles or driving cars when they died in a hit-and-run accident.

Most of the city’s hit-and-run fatalities have been solved, a San Diego Police Department official said.

However, out of the six cases that have happened in 2014, only one driver has been caught.

When we look at the cases from the past five years, we can see that most happened on or near freeways.

According to the National Highway Traffic and Safety Administration, a pedestrian has a 40 percent chance of being killed if he or she is hit by a car traveling 30 mph. If the car is traveling at 40 mph, the fatality rate doubles. If a person is hit by a 50-mph car, the chance for survival is small.

While in the last five years most hit-and-runs have been spread out and have occurred close to interstates, the two ZIP codes with the highest number of hit-and-runs are 91950 and 92102, which cover National City and parts of Golden Hill and South Park. These areas saw four fatal hit-and-runs each.

Still, while factors like car speed, population density and lack of pedestrian-friendly sidewalks may help explain why people are hit by cars, they don’t explain why drivers fled.

Between 2009 and June of this year, five bicyclists and 52 pedestrians were killed by drivers who left the scene.

Looking at these crimes through numbers softens the reality of the deaths involved. Victims are as young as 18 months and as old as 90. Some deaths triggered public outrage. Others, usually involving victims who were homeless or poor, stirred little media attention – if their deaths were written about at all.

Here are those stories.

Gwyneth Shoecraft and Bianca Bruno contributed to this post.

Correction: A previous version of this post incorrectly listed Golden Hill and South Park’s ZIP code. The correct ZIP code is 92102.