Four people were killed after an 18-wheel truck smashed into a row of vehicles that had stopped on a Mississippi Interstate highway to avoid hitting debris spilled by an overturned pickup truck trailer, state police said. A father and his daughter in one car and two young men in another car died in the nearly dozen-car wreck on Interstate 10 in coastal Hancock County, near the Louisiana border, just after midnight, Mississippi Highway Patrol spokesman Johnny Poulos said. "It's a tragic situation," Poulos said. "You have families that are going to be grieving through the holiday period." The crash occurred after the pickup truck with a trailer carrying used computer equipment overturned, littering the highway with debris. Oncoming vehicles ground to a halt to avoid hitting it, and the 18-wheeler plowed into the stalled traffic. Four people also received injuries that were not life- threatening, Poulos said.   Six cars and four trucks were involved in the crash, he said, adding that the highway was closed for several hours. (Reuters)