A 76-year-old Cheyenne man is dead after driving his vehicle into a train northwest of town.

The Wyoming Highway Patrol says David Petersen was headed northwest on Horse Creek Road around 10 p.m. on April 2, when he stopped for a northbound train at milepost 17.03.

For an unknown reason, possibly fatigue or a medical emergency, Petersen allowed his vehicle to roll forward into the side of the train, which was traveling about 45 mph.

The momentum of the train spun Petersen's vehicle clockwise and pushed it off of the road.  The vehicle came to rest about 20 feet north of the road.

The engine of the train had already passed when the collision occurred, so the conductor and engineer were unaware of the incident and didn't stop the train.

It wasn't until 6:16 a.m. the next morning, nearly eight-and-a-half hours after the crash, that Petersen was found lying on the ground next to his vehicle.  Petersen was unresponsive and was pronounced dead at Cheyenne Regional Medical Center.

The Patrol says an autopsy is being conducted to determine if Petersen died as a result of the collision or from exposure.