DURHAM — State troopers have charged a 50-year-old tractor-trailer driver with driving while impaired and three counts of felony death by vehicle following Thursday's afternoon's series of collisions on Interstate 40 that left three people dead.

Ronald Eugene Graybeal of 306 Elana Lane in Newport, Tenn., was charged with being under the influence of drugs at the time of the accident, 1st Sgt. Jeff Gordon, a patrol spokesman, said today.

Troopers searched Graybeal's truck and found two different drugs and drug paraphernalia, Gordon said, adding that he was not sure what those drugs were.

The accident killed the drivers of three other vehicles: John Paul Llanio, 38, of Kannapolis; Barbara Boda Caldwell, 64, of Mebane; and Gary DeWayne Smith, 45, of Burlington.

Emergency workers transported a fourth motorist, Reginald Keith Thompson, 49, of Greensboro, to Duke Hospital where he was treated for injuries not considered life-threatening, Gordon said.

Graybeal is being held in the Durham County jail in lieu of $500,000 bail, Gordon said.

Investigators say Graybeal was driving a 2008 Freightliner tractor-trailer west on the interstate, near the N.C. 15-501 overpass, when he collided with a Ford F-250 pickup truck driven by Llanio. The tractor-trailer continued and then crashed into a 2008 Chevrolet Equinox driven by Caldwell.

The tractor-trailer then slammed into a car that burst into flames. The car, which was burned so badly that troopers could not determine its make and model, was occupied by Smith, Gordon said. The tractor-trailer barreled on before striking a 20-foot box truck that was driven by Thompson, Gordon said.

The Highway Patrol is continuing to investigate the crash. A reconstruction of the accident could take up to four weeks to complete, Gordon said.

thomasi.mcdonald@newsobserver.com or (919) 829-4533