iStock/Thinkstock(SEATTLE) — Authorities are searching for at least one person who opened fire on four cars traveling down Highway 509 near Seattle-Tacoma International Airport.The highway near the airport was shut down for more than five hours while Washington Highway Patrol searched for the shooter Wednesday afternoon.Seattle resident Mary Ertl’s windshield was one of those struck.“I heard a boom, and then glass all over my face,” Ertl told ABC affiliate KOMO-TV. “I thought it was a rock until I looked at the passenger side, and then I knew it was a bullet.”Although no one was hurt, the western-most runway at the airport also was temporarily closed as a precaution. The highway later fully reopened.Investigators told KOMO-TV the shooter likely was on foot, on the side of the highway, based on the trajectory of the bullets. Each vehicle was hit on the driver’s side.“When we’re arriving at things like this, we are putting on our active-shooter gear — which is a blessing to have — the heavier vests that stops rifles and helmets,” trooper Rick Johnson told KOMO-TV.Copyright © 2018, ABC Radio. All rights reserved.