A Haverhill man was killed after the car he was driving flipped over and was struck by a tractor-trailer on I-495 in Lawrence around 2 a.m. Saturday, State Police said. Carlos V. Cunha, 55, was driving a 2004 Buick LeSabre that rolled over and landed in the left and middle lanes, just before exit 42B, State Police said in a statement. After the roll-over, a tractor-trailer struck the car. A few passing drivers called 911, said Trooper Dustin Fitch, a State Police spokesman. The driver of the tractor-trailer called police after he hit the car. When police arrived, Cunha, who had been ejected from the car, was pronounced dead. The tractor-trailer driver was not injured and has not been charged, Fitch said this morning.