The infant's parents were on their way to Madigan Army Medical Center in Seattle, but discovered their soon-to-be-born daughter couldn't wait that long, according to Trooper Guy Gill.
The State Patrol started receiving calls about the family's Dodge Challenger driving erratically and at high speeds. The father also called, letting authorities know about his expectant wife.
The Dodge pulled over twice, and the infant was successfully delivered on the second stop.
State troopers and the West Pierce Fire Department were called to the scene.
"By the time we got there, all that needed to be done is cut the umbilical cord," Gill said. "The child was already born, looking great."
The family was taken to Madigan.
"It's a happy story," Gill said. "These are the type we don't see too often ... everyone is doing well."