Officers from the CHP and the Riverside Fire Department responded to a report of a baby being born on the freeway north of Eastridge Avenue at around 2:35 a.m. Saturday.
When authorities arrived, the baby boy had just been delivered with the help of his grandmother and his aunt.
The woman, her mom and her sister were on the way to the hospital, but when they were about 15 minutes away, the baby decided he couldn't wait.
"All of a sudden, she started screaming, saying, 'Mom, pull over! His head's coming out. Pull over!' And I just kind of pulled over here a little bit, off the road. And then we got out, and the head wasn't out yet, but she could feel it. And then I got the blanket around her, and my other daughter says, 'Oh my gosh, I see the head.' That's when I said, 'Get out of the way,' and I put my hands down under her and I helped guide the baby out and I delivered him," the baby's grandmother said.
The father, along with firefighters and CHP officers, arrived not long after.
The mom and the baby, whom they named Jackson Garrett, are both doing well at the hospital, officials said.