FOND DU LAC COUNTY, Wis. (WTAQ) - Fond du Lac County authorities say fog might have helped cause a traffic crash that killed a 56-year-old Cudahy man. Officers said Mark Heller died after his car collided with a tractor that turned in front of him. There was only about 200 feet of visibility at the time of the crash, which happened Tuesday morning on a county road near Alto. The tractor was turning into a driveway, and it was pulling a feed wagon. Its driver was not hurt. Authorities said the car started on fire after it got wedged under the tractor. The accident remains under investigation. Mark Heller is the son of former Fond du Lac police chief and current county board member Mel Heller.