Troopers from the Frederick barracks said four people, including two who were thrown from the car, were injured in the first crash just past Keep Tryst Road.
Police said five people involved in the second crash were taken to area hospitals, including Washington County Hospital and Frederick Memorial Hospital, following the second crash on U.S. 340 at Keep Tryst Road. Seven others refused medical treatment at the scene, troopers said.
Police said that in the first crash, the driver of a Geo Metro lost control of the car and hit a guardrail.
Trooper Jim Ardinger said two passengers were thrown from the back seat of the Metro, including one who was thrown over a guardrail and down a bank.
The second accident was near a bend in the road where oncoming cars might not have been able to see cars stopped ahead because of the first accident, said Scott Osborne, a paramedic with Boonsboro Ambulance & Rescue Inc.
Ron Lowe, of the Brunswick Engine and Truck Co., said he was setting up warnings for motorists approaching the first accident when the second crash occurred.
Six vehicles, including a passenger car, a pickup truck, a sport utility vehicle and a pickup truck with an attached trailer were involved in that pileup.
Trooper Andrew Smith of the Hagerstown barracks said a Tennessee man, who was driving a Dodge pickup truck that was hauling a 24-foot trailer, was charged with negligent driving in connection with the pileup.
Smith said the pickup crashed into several cars that were stopped, some for several minutes, because of the previous crash.
"He was bouncing around from the fast lane to the slow lane, smashing into cars," Smith said.
Smith said all of the injuries in the six-vehicle pileup were considered minor. He said the most serious were to a six-month pregnant woman.
Traffic was backed up on eastbound U.S. 340 for several miles following the crashes. Several motorists said they either saw or just missed being involved in the pileup.
Steve Grams, of Frederick, pointing to the pickup truck with the attached trailer, said, "I heard this truck skidding behind me. When I got out of the car, people were trying to get out of their cars and some guy was stumbling around and collapsed."
Lisa McConkey, of Middletown, Md., said, "We're really shaken up. I don't know how we didn't get hit by the pickup with the trailer. It's the scariest thing I ever ... I thought we were going to die."
Dozens of firefighters were on the scene helping clean up glass and metal thrown from the vehicles in the pileup.
Several ambulances and tow trucks could be seen driving along U.S. 340 and on Md. 67.
Bobby Webster, the assistant store manager at a Sheetz convenience store in nearby Knoxville, said he heard that the accident was causing two- to three-hour delays.
Webster said a store employee called from the accident and "She said it was going to be about two hours ... Another customer said it was to be about three hours."
Just before midnight, emergency responders dumped piles of brown sand onto the fluid-soaked roadway.
Smith said police anticipated eastbound U.S. 340 would reopen at about midnight.
Staff writers Gregory T. Simmons and Dave McMillion contributed to this story.