Thursday's accident, which also injured four people, occurred shortly before 5 p.m. in the northbound lanes of I-81 where traffic goes to one lane due to highway construction.
The tractor trailer driver, Raymond Ramon, 49, of Florida, was traveling north when he came to the other traffic, slowed by the lanes narrowing to one lane, police said.
Ramon tried to stop, but slid into a pickup truck driven by James Brice, flipping the truck over into a ditch, police said.
The Ford pickup exploded into flames, police said.
Brice, 28, worked at Jefferson Distributing Co., in Martinsburg, Humphrey said. A car in front of the pickup truck also was struck by the tractor trailer, police said.
Three people in the car, Mary Thomas, 65, of Williamsport, and passengers Cathy Miles, 35 and Kellie Miles, 12, were injured. They were all taken to Washington County Hospital.
As of late Friday, Thomas was in fair condition in intensive care, according to a hospital information clerk.
Cathy Miles was in good condition, she said. Kellie Miles was in fair condition.
Ramon was taken to City Hospital in Martinsburg where he was treated and released, police said.
The wreck blocked the northbound lanes of the interstate for nearly three hours and caused major traffic jams in Martinsburg as highway traffic was detoured through the city.