A Greyhound bus carrying 42 people tipped over as it drove down a northwestern Indiana interstate Tuesday, injuring more than two dozen aboard, officials said. Police said the driver probably fell asleep.

None of the injuries appeared to be life-threatening, police said. About 25 passengers were being treated at two hospitals and more were taken to a third, spokespeople for the hospitals said.

State Police Sgt. Ann Wojas said driver Darren P. Duke, 46, of Indianapolis likely fell asleep at the wheel of the bus as it traveled south on Interstate 65 about 15 miles south of Gary. He told investigators that he began his day in Indianapolis about 2:30 a.m. Eastern time, drove to Chicago and was on a return trip about 7 1/2 hours later when the crash happened on the clear, dry roadway.

Witness Douglas Judy of DeMotte said he was north on the interstate when the bus crashed in front of him.

"The bus drifted right into the gravel and then fishtailed and overcorrected and then it hit the (center) wall," Judy told The Times of Munster. "It was going at such a high speed it was airborne. I thought it was coming over the wall at me.

"The driver just lost control," he said. "There wasn't any car in front or in back of him."

The bus ended up on its right side, with its wheels against the concrete barriers in the highway's median. The crash caused police to close all southbound lanes of the interstate, with northbound lanes remaining open.

Greyhound spokesman Dustin Clark said Duke has driven for the line for about 18 years, had a good driving record and did not exceed his federal limit of 10 hours behind the wheel within a 15-hour workday.