The lone bus belonging to a mom-and-pop tour operator veered off an interstate and overturned early Saturday, killing 15 Chicago area travelers on their way to a Mississippi casino. Witnesses told police the bus, which carried family members and friends of the tour company owner, was drifting on the road.

The bus was about 30 miles short of its destination in Tunica, Miss., when the crash occurred about 5 a.m. on Interstate 55 in northeastern Arkansas, near Memphis.

All of the 16 surviving passengers were injured, many of them critically. Some of the dead were found crushed beneath the bus after wrecker crews pulled it upright, Bill Sadler, an Arkansas State Police spokesman, said.

Among the dead were Herbert Walters, the bus owner's brother, who had been driving, and Mareen Walters, the owner's wife, as well as the owner's stepson and niece.

Witnesses told police the bus drifted off the road near a point where the interstate veers to take travelers into Memphis.

The impact tore off a section of the bus's roof, and emergency workers had to shear off the rest of the top to reach a trapped passenger.

Tracks in the grass showed the bus went straight rather than around the curve, then hit a ditch and flipped over. There were no skid marks.

Other victims, thrown from the bus, were scattered among grass and weeds at an interstate exchange, along with popped-open suitcases and other belongings.

Sadler said 14 people died at the scene. Hospitals reported receiving a total of 17 people, including one who later died.

The Arkansas State Police said the tour bus flipped over after the driver apparently failed to navigate a curve en route to a Mississippi casino. Fifteen people were killed; 16 were injured.