Caddo sheriff's deputies are investigating a bad wreck involving an 18-wheeler and a passenger car on I-49 southbound between Bert Kouns and Southern Loop.  Southbound lanes of I-49 are shut down at Bert Kouns and traffic is being diverted.  Deputies are diverting southbound traffic over to Linwood until the investigation is complete and the wreckage can be cleared.  That is expected to take several hours.  The wreck happened around 10:15 this morning when a northbound passenger car crossed the center median and slammed into a southbound UPS tandem 18-wheeler, knocking it onto its side.  The driver of the car was air-lifted to LSU-Hospital, one passenger was taken to LSU by ambulance, and another passenger was pronounced dead at the scene.  The truck driver was not hurt.