Two were injured, including a woman who was airlifted to Harborview Medical Center, after a three-vehicle accident in Federal Way Thursday on southbound Interstate 5.

According to a Washington State Patrol spokesman, a motor home on the freeway crashed into a car and pushed the car beneath a box truck. The passenger of the car was taken by helicopter to Harborview while the car’s driver, who had less serious injuries, was transported by ambulance. A spokesman with South King Fire and Rescue, who responded to the accident, said one of the injured sustained “life-threatening traumatic injuries.”

No one else was injured.

Washington State Patrol said the motor home driver was not impaired and said detectives were investigating other potential causes.

Southbound I-5 was completely closed following the accident, which occurred around 1 p.m. Lanes opened one by one between about 2 p.m. until about 5:45 p.m., according to the State Patrol, when all lanes were reopened.

Traffic forced off I-5 was met by Federal Way’s usual rush hour, resulting in long delays and backups throughout the city.