A fifth person in the car also was killed.
The driver of the tractor-trailer -- Ejub Grcic, 54, of West Valley, Utah -- was charged with homicide by vehicle and other counts after Monday afternoon's crash, police said.
A fifth count of homicide by vehicle was expected to be filed Tuesday, state police Trooper Rob Lagoon said.
State police said four people died at the scene -- Janet A. Kerr,35; Kathleen A. Kerr, 13; Kenneth E. Kerr III, 4; and Alessandra S.Hall, 16; all of Smithfield, N.C.
The driver of the car, Kenneth E. Kerr Jr., 35, also of Smithfield, N.C., died about 7 a.m. Tuesday, police said.
The family apparently had been visiting area relatives over the Independence Day holiday.
The big rig collided with the car on state Route 8 in SlipperyRock Township, about 45 miles north of Pittsburgh, Lagoon said.
According to state police, the car apparently struck the tractor-trailer's fuel tank, causing both vehicles to burst into flames, state police said.
Grcic, who did not speak English, was arraigned and placed in the Butler County Jail on a $50,000 bond.
A woman who answered the phone at a number listed for Hajna Grcic inWest Valley City, Utah, identified herself as Ejub Grcic's daughter. She said the family did not have an attorney and declined further comment to The Associated Press.
Retired truck driver Merlin Batykefer Sr., 71, who lives across the street from the accident site, said he heard the collision and started running. When he and his son arrived, they saw the driver of the car crawl from beneath the fiery wreckage.
"We got the fire out and put him here in the yard," Batykefer said. "There was just a lot of banging and booming out there when it was going on."
Kenneth Kerr asked about his family, Batykefer said.
"He started talking about his family, and I thought they were all inside of the truck," Batykefer said. "He said: 'No, they were in my car.'
"It is just something I don't want to see again."
Although some residents said the intersection has been the sceneof other crashes, including fatal ones, state Department ofTransportation spokesman Jim Struzzi said the agency had notreceived any complaints about it.
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