Officials say the Cessna propeller plane landed in an open field, but then crashed through a fence and out onto Route 1, crossing the southbound lanes.
Cars swerved to avoid the plane. The Air Force says a 2005 Hyundai Elantra driven by Katie R. Torbert, 32 of Fawn Grove, Pa., hit the center guardrail.
Torbert and her four passengers, ages 14, 14, 10, and 4, were all unhurt.
Traffic was down to one lane for more than two hours.
The 54-year-old instructor and 44-year-old pilot on the plane both escaped injury.