Durham, N.C. — A truck driver faces an impaired driving charge after his tractor-trailer slammed into a Durham police cruiser on the shoulder of Interstate 85 Wednesday afternoon, police said Thursday.

Officer Teresa Gilliam had stopped a 2010 Mazda 3 on the right shoulder of the highway at about 3:15 p.m., just past the exit ramp for Cole Mill Road, police said. A tractor-trailer hit Gilliam's unmarked car from behind, forcing it into the Mazda.

"She was getting ready to get out, and the 18-wheeler was swerving, and he hit her and spun her," witness Amanda Chavez said. "When I got over to the cop car, she was laid over. She wasn't conscious."

Gilliam was taken to Duke University Hospital, where she is listed in critical condition.

"Her spirits are good. She’s very positive. She has always been and will continue to be a very strong officer," Lt. Patrice Andrews said.

The driver of the Mazda, Robin M. Gee, 50, of Greensboro, was treated at Duke Hospital and released.

The truck driver, Charles Edward Caldwell, 44, of Roberta, Ga., wasn't injured in the crash, but he remained at Duke Hospital on Thursday after complaining of a health condition during police questioning.

Caldwell has been charged with driving while impaired and careless and reckless driving.

The citation notes that Caldwell's truck was traveling 70 mph, which is 10 mph faster than the speed limit on that stretch of I-85, and was swerving between lanes. It also notes that Gilliam had activated the blue lights on her car but that Caldwell failed to move out of the right lane, as required by state law when passing a stopped law enforcement vehicle.

Officers noted that Caldwell's eyes were droopy and his speech slurred, and police took a sample of his blood to test for alcohol or drugs.

A representative of Rockey's Moving and Storage in Killeen, Texas, said Caldwell had been driving for the company since May and had no previous problems.

Federal motor carrier safety records show Rockey's Moving has had three other accidents in the last two years, but no one was injured in any of those crashes.

“This is a total surprise. We’ve never had an incident like this in the history of the company. It’s very unfortunate. It’s very unfortunate for the officer. Our prayers go out to the family," said the company representative, who declined to give his name.

Gilliam has been with the Durham Police Department since 1997.

"We’d like to say thank you to the citizens that actually stopped to render aid to Officer Gilliam," Andrews said. "We really have been humbled by the appreciation and the gratitude that have just been coming in (and) the prayers."