HARRISBURG, Pa. >> Investigators looking into a dead-of-night bus crash over the weekend on the Pennsylvania Turnpike have identified the five people killed, but it may take much longer before they will able to say what caused the pileup that also left dozens injured.

The National Transportation Safety Board plans to discuss the investigation at a news conference scheduled for later today.

Their focus will almost certainly include a close look at the driver, Shuang Qing Feng, 58, who was thrown from the bus and died at the scene early Sunday, on Interstate 76 in a mountainous and rural area about 30 miles west of Pittsburgh.

The great majority of all vehicle crashes involve some sort of driver behavior, said Christopher Turner, director of crash and data programs for the Commercial Vehicle Safety Alliance.

The loaded bus, which state police said was operated by Z&D Tour Inc. of Rockaway, New Jersey, went out of control on a downhill slope, striking the center barrier twice and setting off a chain reaction in which the bus was struck by two trucks, state police said. Two occupants of one of the trucks, UPS employees from central Pennsylvania, also were killed.

“This is not a typical incident — buses overturning is not a common occurrence,” Turner said. “But obviously the risk is tremendous.”

The bus was traveling from the New York area to Cincinnati when the wreck happened around 3:30 a.m. Sunday.

Several messages seeking comment from the company were not returned, but Z&D owner Chen Dan Yu told The New York Times the bus had left New York’s Chinatown for a regular route to Ohio.

Chen told the paper that weather was to blame. “It suddenly started to snow,” he said.

Federal records indicate no incidents in the past two years that resulted in a company’s bus being taken out of service.

Mount Pleasant Township Fire Chief Jerry Lucia, among the first to arrive at the scene, encountered dazed victims who had already been able to get out of the wreckage. The road was wet after being treated with road salt following about an inch of snow some four or five hours earlier, he said.

“My rescue engine was on the scene right before me,” Lucia said today. “When they got out of their vehicle they came upon 40-some people standing along the road with no shoes on, freezing cold.”

Lucia said he thinks many of the passengers had been asleep.

“They were all together,” Lucia said. “They were helping each other to keep calm and cool and collected.”

Many, if not most, did not speak English, he said. Rescue crews assembled them about 50 feet away from the crash, and medics began treating the wounded, getting the most seriously injured into ambulances. Because the crash had shut down the turnpike, emergency crews had to drive the wrong way down 5 miles of highway to reach the scene.

Turnpike officials shut down the highway and took out a section of guardrail so that westbound vehicles could be turned back east for eventual exit, Lucia said. Fire crews worked to contain spilled diesel fuel, he said. One firefighter injured an ankle while searching the wreckage for victims.

About 60 people were injured, flooding hospitals with a range of injuries. Authorities have said all patients are expected to survive.

It was some 13 hours after the crash before the eastbound lanes could be reopened.

Feng and two other victims are from New York City: passengers Eileen Zelis Aria, 35, and 9-year-old Jaremy Vazquez, according to the Westmoreland County coroner’s office.

The two UPS employees killed are Daniel Kepner, 53, and Dennis Kehler, 48.

The cause of the crash is still unknown, and a Pennsylvania State Police spokesman said it could take weeks or months to determine.