A single-vehicle crash about one mile west of Fallon in Prairie County killed a man and seriously injured a woman.
Prairie County Undersheriff Greg Huber said Saturday night that the names of the man and woman have not yet been released.
Montana Highway Patrol Trooper Jason Dulin said the driver, an 86-year-old man, and the passenger, an 81-year-old woman, both of Savage, were traveling eastbound on Interstate 94 at about 8:20 p.m. Friday in a Buick LeSabre.
For unknown reasons, the car veered off the eastbound lane at the Fallon Creek Bridge and struck the guard rail.
The man was pronounced dead at the scene and the woman was transported by ambulance to Glendive Medical Center for serious injuries.
Dulin said the woman was later flown to a Billings hospital.
The cause of the crash remains under investigation, Dulin said. He does not believe alcohol or speed were factors in the crash.
Neither the man nor the woman were wearing seat belts, he said.
The road conditions were dry.