Beaver, who has driven charter buses for six years, said he steered over to the west edge of the southbound lanes to avoid a stopped red Geo Prism, but hit the car in the back as the tractor-trailer pushed the bus down the interstate.
The Prism's driver, Joe Wert, of Cedar Grove, Tenn., said he, his wife and their two small children were not injured.
The tractor-trailer driver, Donnell Reece Kery, 22, of Los Angeles, was charged with failure to reduce speed to avoid a collision, Keller said.
Neither Kery nor his passenger, Kap Fonua, were injured. Fonua said he was asleep in the bunk when the accident occurred.
The driver from the first wreck that caused the initial traffic backup was taken to City Hospital after the car went out of control, hit the median and flipped over, said Deputy Richard Burrell.
That driver, Lucius Roundfield, of Falling Waters, was in critical condition in the Intensive Care Unit at City Hospital on Sunday night, a hospital spokeswoman said.
No charges had been filed against Roundfield as of Sunday night, Keller said.
Fanua said he and Kery were hauling rolls of paper from Harrisburg, Pa., to Georgia when the accident occurred. Some paper rolls spilled out of the front of the trailer, which was ruptured, and were leaning against the back of the cab. The two work for CRST Inc., of Cedar Springs, Iowa.
The lower back of the bus was pushed in where the tractor-trailer hit it.
The hazardous materials unit from Berkeley County sprayed sand on the southbound lane where diesel fuel spilled from the tractor-trailer's ruptured fuel tanks, Robinson said.
Three of the bus passengers were taken out of the rear of the bus on backboards through windows that rescue officials propped open, said Fire Chief Robert Robinson with Bedington Volunteer Fire and Rescue.
"All the seats went back and all the injuries were back and neck injuries," Robinson said. Those injured were in the very front or back of the bus, where four seats had to be bent back up to remove injured passengers.
Most of the patients were able to move "real good," Robinson said.
"It could have been bad, but it wasn't," Robinson said. "We had good communication." Robinson said he had about 50 rescue personnel and at least seven fire and rescue companies respond, including units from Bedington, South Berkeley, Hedgesville, Jefferson County, Williamsport, Md., and Halfway, Md.
There was at least a one-mile backup on southbound I-81, which was still closed at the accident scene as of midnight Sunday, according to West Virginia State Police.
Atlantic Coast Charters, of Hagerstown, Md., brought a second bus to take the senior citizens back to Martinsburg. They were originally scheduled to be dropped off at Weis Markets on North Queen Street.
After eating in Gaithersburg, Md., the group spent the day in the nation's capital seeing the U.S. Army Band holiday concert at the Washington Theater and later driving around the White House, the U.S. Capitol and the Mormon Tabernacle to see the Christmas lights, bus passengers said.
A Martinsburg man, who was a passenger in the bus, described feeling a "jolt" when the tractor-trailer hit the bus.
"We just felt a bump and we didn't know what had happen," said bus passenger Mildred Horner, 84, of Martinsburg.
Of the 10 bus passengers taken to City Hospital in Martinsburg only one patient was expected to be admitted, said hospital spokeswoman Christy Polak. That patient was a 81-year-old Falling Waters man with injuries to the head, hip and chest, she said.
In preparation for the patients, the hospital initiated a disaster/emergency plan which involved calling in additional staff and bringing in more equipment, she said.
Four bus passengers were taken to Washington County Hospital, where they were treated and released, a hospital spokesman said.