A New Bedford teenager was killed yesterday morning in a single-car rollover on Route 140 northbound, State Police said. The 17-year-old was riding in the back seat of a 1990 Honda Accord when the 19-year-old driver, also of New Bedford, lost control at about 7:30 a.m. The car rolled over several times into the median of the highway. The victim, who was not wearing a seat belt, was thrown from the vehicle. A New Bedford 17-year-old who was riding in the front passenger seat and the driver were taken to Rhode Island Hospital with minor injuries. The back seat passenger was pronounced dead there. No names were released.