Troopers said the the impact was so hard that one of the tires on the lawmower flew into a neighboring yard.
Investigators are trying to determine how close the mower was to the highway and what caused the driver of the minivan, a 72-year-old woman, to lose control.
Authorities said a second crash happened involving a motorcycle as a result of a traffic backup on Route 68 due to the lawnmower crash. Careflight was called and took the motorcyclist to Miami Valley Hospital.