Eavey's cycle also went into the eastbound lane and she was thrown onto the roadway when it struck the van, he said.
The accident occurred on a curve about a tenth of a mile west of the Md. Route 144 junction, according to Maryland State Police.
The driver of the van, Candace Garrett Taylor, 48, of Mifflintown, Pa., was taken to Washington County Hospital as a precaution, but she was not seriously injured, Embly said. She was still being evaluated in the emergency room at 11:30 p.m.
A passenger in the van, Paul Allen Walter, 30, also of Mifflintown, was unhurt, according to the trooper.
The accident closed National Pike for approximately 2 1/2 hours for the investigation and cleanup of the crash scene, according to state police.
Diane Williams of Clear Spring was visiting her fiance's parents at 16960 National Pike when she heard wheels screech loudly and two vehicles collide at about 7:15 p.m. She ran outside while her fiance, John Cook, called 911.
She said she saw two bodies, one lying underneath the van and the other in the middle of the street. Both still had their helmets on, she said.
"You could just see a leg coming out near the front wheel underneath the van," she said.
"She got thrown real bad," said Mark Grove, who also was visiting the house and witnessed the scene after the accident.
The van's front grille was caved in about two or three inches, and the motorcycle involved in the accident lay almost crushed about six or seven feet in front, said Ethan Croutch, who lives down the street from where the accident occurred.
None of the other motorcyclists were involved in the accident, Embly said.
Witnesses said accidents are infrequent in that area.
Staff Writer Vandana Sinha contributed to this report.