(Barnhart) A Desoto man was killed on Christmas Day in a traffic accident on Interstate 55 in Jefferson County. The highway patrol says a motorcycle operated by Leon Barnett was traveling at a low rate of speed in lane 3 of northbound I-55. A second vehicle, driven by James Mattingly of Herculaneum was in the second lane when he tried to change into lane 3 and the front of his vehicle hit the back of the motorcycle. Barnett was thrown from the motorcycle and killed in the accident. Mattingly suffered minor injuries. The accident took place at 2:16 Wednesday afternoon and closed traffic along I-55 northbound for several hours.