The suspect is described as a man between the ages of 25 and 35 years of age, according to police.
He was described as possibly Hispanic or Portuguese with short dark hair, receding on the sides, creating a widow's peak, police said.
The suspect was driving a white 2010 or newer vehicle with large polished chrome rims, police said.
The incident occurred shortly before 5:30 a.m. Thursday on southbound I-680. Both drivers exited at Mission Boulevard and turned right onto Brown Road, and one driver fired a gun at the other car, hitting the driver, according to police.
The shooter then fled and has not been located by police.
The victim, a 59-year-old Pleasanton man, managed to drive several blocks and stopped near the East West Bank at 44615 Mission Blvd., police said.
He suffered at least one gunshot wound to the abdomen and was taken to a hospital. His wounds are considered serious but not life-threatening.
Anyone with information on the shooting or the suspect is asked to call Fremont police at (510) 790-6900.