On August 26, 1999, at 1045 central daylight time, a Cessna 172M, N61612, sustained substantial damage while taxiing on a roadway for departure, near Bloomington, Illinois. The airline transport pilot reported no injuries. The personal 14 CFR Part 91 flight was operating in visual meteorological conditions. No flight plan was on file. The flight was originating at the time of the accident with the intended destination of Saint Louis, Missouri. The airplane was landed on the road in a precautionary landing following a rough running engine. The pilot obtained the services of a mechanic to repair the airplane's magneto. After the repairs were completed, the pilot was taxiing the airplane for departure when both wings were damaged when they impacted road signs on each side of the roadway. Witnesses saw the airplane approaching the signs; however, had no way of warning the pilot who did not see them prior to impact.