Truck driver, passenger suffer serious injuries.
ATV failed to make turn, struck tree.
Crash is under investigation.
Driver was not wearing seatbelt.
ATV was traveling on roadway without lights.
Florida Highway Patrol investigating accident.
Fatal accident is latest involving County Road 337.
Woman was driving wrong way on U.S. Highway 301.
FHP investigating cause of accident.
Single-vehicle incident is still under investigation.