Among the issues investigators will be looking into are whether the driver was cut off by another vehicle, whether he fell asleep at the wheel, or whether drugs or alcohol may have been involved.
The driver, who suffered a gashed arm, told state police another driver cut him off.
Three people remain hospitalized after the Canadian tour bus overturned, injuring nearly two dozen people overall.
A spokeswoman at St. Joseph's Regional Medical Center says the three were in fair condition Sunday, but declined to provide further details on them or their injuries.
State police say 23 people - including the driver and two young children - were hurt in the accident. There were 57 passengers aboard the bus, which left from Toronto and was bound for New York City.
The accident happened at about 7:45 a.m. when the bus overturned on a highway exit ramp and slid down an embankment.
Police believe the driver was travelling at a high rate of speed, and was unable to negotiate the curve coming off the exit ramp.
Some windows burst during the collision and the frames pinned three people, but they were quickly freed and taken to hospitals with the other victims.
The bus was chartered by Cynthia Tours based in Toronto. The passengers were a mix - some were part of a church group, others were coming down to visit family. There were also drop off locations in both Manhattan and Flatbush. The bus was attempting to come over through that overpass when it skidded into a muddy ditch.
"I just felt a big boom, people started flying," said passenger John Anthony.
Anthony was the first to climb out of the broken front windshield of the Canadian Tour Bus and call for help. He took pictures of the frantic rescue.
All 56 people on board left Toronto at 6 p.m. on Friday evening. They passengers had plans to spend their three-day Canadian Thanksgiving holiday weekend in New York. The bus then lost control and flipped over near Exit 53 on I-80 East in Wayne around 7:40 Saturday morning.
That is when passengers sprang into action. Warren Lawrence helped 15 people out of a rooftop hatch.
"The bus was lying on its side - people want to get out," Lawrence said.
The accident backed up traffic in the area for hours while law enforcement officials and emergency services vehicles attended to the scene.
Several highways connect there, and the area is known locally as the "spaghetti bowl".
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