According to the California highway patrol, the victim was walking northbound along the Cedar overpass with two friends, both 12-years-old, when she chose a different route.
Sgt. Jeremy Key said, "13 year old decided she wanted to meet the other two on the other side, but go underneath the freeway and take the freeway route."
The girl accessed the freeway from this embankment, which is partially blocked off by a chain-link fence.
"This is a steep embankment and it's unsafe anyway. This moving traffic, you never see anybody walking on the freeway, and there's a reason because you're not supposed to be."
The girl made it across just one lane of the 180-168 interchange, before she was hit. Officers say, they're not sure why the girl took such a dangerous risk.
Sgt. Jeremy Key said, "As far as her friends know, she just took the initiative and started walking on her own, said she would meet them on the other side, just out of the blue."
As for the driver, that person stopped and immediately called police. Investigators do not believe drugs or alcohol played a role in the crash.
The girl's identity has not been released.