At least two people were killed in northeast Houston on Wednesday when their vehicle veered across several freeway lanes, struck the back of a police car and plunged over the side to the pavement below, police said. A Houston police officer had made a traffic stop in the left lane of U.S. 59 southbound between Kelly and Crosstimbers about 4:30 p.m., police said. Main lanes were closed for four hours, causing a traffic backup for miles.