The woman, Dorothy Brisko, was first struck while walking on I-81 southbound near Maugans Avenue. After being hit, she walked back out into traffic and was struck a second time by another tractor trailer.
North and southbound lanes were closed while the Maryland State Police helicopter arrived on scene.
Brisko was taken to Baltimore Shock Trauma, where she remains in critical condition.
The Washington County Sheriff's Department, Maugansville Fire and Rescue, Halfway Fire and Rescue, and police assisted at the scene. An investigation into the incident is continuing.