On May 2, 1999, about 1245 Eastern Daylight Time, a Cessna 172, N5815E, was substantially damaged while taxiing at the Port Columbus International Airport (CMH), Columbus Ohio. The certificated private pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 CFR part 91. According to the pilot, she requested a progressive taxi to Runway 10L from the ground controller. The controller told her to taxi south, out of the "Airnet ramp", and make a left turn to the east, onto Taxiway Charlie. The pilot taxied south, and noticed a "C" (charlie) taxiway sign. She made a left turn onto a perimeter road, instead of the taxiway. After the left turn, the left wing of the airplane struck a fence. The pilot further stated that she had never been to CMH before. A review of photographs revealed that their was no sign identifying the perimeter road. However, the road is marked by dashed white lines at the center. Additionally, the airport diagram used by the pilot did not depict the perimeter road. Examination of the airplane by a Federal Aviation Administration Inspector did not reveal any pre-impact mechanical malfunctions, nor did the pilot report any. The Inspector observed spar damage to the left wing. According to representatives from the CMH Port Authority, the perimeter road has been in place for approximately 2 years. During that time, there have been no other known incidents or accidents in which a pilot mistook the road for a taxiway.