The accident happened at around 6 a.m. Saturday near the Pennsylvania Turnpike's Lebanon-Lancaster exit. Fourteen of the 18 people aboard were injured, but all were treated and released from hospitals and eventually continued on their journey, said Maureen Richmond, a Greyhound spokeswoman.
The 24-year-old driver, Kareem Edward Farmer, lost control while traveling in the passing lane, state police said. The front end of the bus struck a concrete barrier and the left rear side rode up against the barrier, state police said. The bus then crossed over the travel lanes, struck an embankment and traveled up the embankment before flipping onto its left side.
A telephone number for Farmer, of Philadelphia, could not be located by The Associated Press. A message was left at his father's home.
Farmer was cited with two summary offenses for not staying in his lane and causing a commercial vehicle to overturn, state Trooper Glenn Fields said. Investigators found no evidence that Farmer was under the influence or that he was over his allowable number of hours driving, Fields said.
Farmer has been driving for Greyhound since March and had received only positive performance evaluations, Richmond said. He had not been involved in any previous accidents with the company.
Dallas-based Greyhound said it was looking at all possible factors as it tried to determine what happened, including interviewing Farmer and passengers, looking at readings from the vehicle's GPS system and inspecting the bus, which is now in Richmond, Va. No immediate determination was made about what happened, Richmond said.
"We're looking at all aspects," she said. "We're really taking everything into account."
A message left Monday with the National Transportation Safety Board was not immediately returned.
The bus originated its trip in New York City and had stopped in Philadelphia. It was on its way to a stop in Columbus, Ohio, when it overturned.
Unlike most of the other bus crashes along the East Coast this year, Saturday's accident involved a commercial carrier, rather than a chartered tour bus or a smaller operator.
More than 30 people have been killed and more than 300 injured in tour bus accidents this year, according to Advocates for Highway and Auto Safety. That is more than in all of the last year, when 30 were killed and 272 injured in 28 crashes.