On March 3, 1995, at 1728 eastern standard time, a Piper PA-28- 140, N7498R was substantially damaged following a collision with light poles and street signs during a forced landing attempt to a highway near Charleston, South Carolina. The commercial pilot and his passenger received minor injuries in the accident. The aircraft was being operated under the provisions of 14 CFR Part 91 by the pilot. Visual meteorological conditions existed at the time of the accident, and no flight plan had been filed for the flight. The flight departed Elizabeth City, North Carolina at 1430, and was destined for Savannah, Georgia at the time of the accident. The pilot reported that he obtained fuel in Elizabeth City, North Carolina. He reported that he burned about 10 gallons of fuel from the right tank and then switched fuel tanks. After flying for about one hour and burning about 10 gallons of fuel from the left tank, the aircraft engine began to run rough. He stated that the first indication of trouble was an unusual noise in the engine compartment, followed by a drop in fuel pressure. He stated that after the fuel pressure dropped, and the engine began to run rough, he switched to the right fuel tank. He stated that the engine continued to run rough, and that the engine eventually lost all power. He attempted an emergency landing on a highway. He stated that he struck some trees, and crashed into the terrain during the final descent into the highway. Examination of the aircraft fuel selector valve revealed that the detent washer was broken and one fourth of the washer was missing. When the selector was rotated, there were no noticeable detents, and the selector was easily rotated to an in-between tanks "off" position.