On April 15, 2015, about 1900 central daylight time, a Universal Stinson 108-1, N9799G, was substantially damaged when it contacted a vehicle during a precautionary landing on a road near Macon, Mississippi. Neither the private pilot onboard the airplane nor the driver of the vehicle were injured. The airplane was owned and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which departed Macon Municipal Airport (20M), about 1845 and was destined for a private runway also located in Macon.The pilot reported that he was nearing his destination when the engine began to run rough. Realizing he would not be able to reach the runway, he elected to perform a precautionary landing to a nearby road. The pilot stated that, throughout the landing approach, he did not observe any traffic on the road; however, the airplane touched down and came to rest on top of a truck, resulting in substantial damage to the fuselage and right wing strut. The pilot did not indicate whether he had applied carburetor heat during the flight. There was no examination of the airplane or engine following the accident. The pilot reported that he departed on the flight with 30 gallons of fuel on board. The pilot held a private pilot certificate with a rating for airplane single-engine land. His most recent Federal Aviation Administration third-class medical certificate was issued in January 2015. He reported 673 total hours of flight experience, of which 570 hours were in the accident airplane. The tailwheel-equipped airplane was manufactured in 1947 and was equipped with a Franklin 6A4-150-B3, 150-horsepower reciprocating engine. The pilot reported that the airplane's total airframe and engine time was 1,101.7 hours. The most recent annual inspection was completed on February 16, 2015, about 11 flight hours before the accident. The weather conditions reported at Golden Triangle Regional Airport (GTR), Columbus, Mississippi, at 1850 included wind from 170° at 6 knots, 10 miles visibility, scattered clouds at 6,000 ft above ground level, temperature 24°C, dew point 17°C, and an altimeter setting of 29.98 inches of mercury. A carburetor icing probability chart indicated a potential for serious icing at glide power given the atmospheric conditions present at the time of the accident.