On August 22, 2020, about 1735 eastern daylight time, N86602, an Aeronca 11AC airplane, was substantially damaged when it was involved in an accident near Nebo, North Carolina. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot was hired to transport the airplane to another state. In preparation for the long flight, he topped the main and auxiliary fuel tanks with fuel (though a gallon of fuel was spilled in the overall fueling process). He then departed utilizing fuel from the 15-gallon main tank. About 45 minutes into the flight, the engine began to run rough, and the pilot said he could smell a strong odor of fuel in the cockpit. He applied carburetor heat and pumped the throttle several times, but to no avail. The pilot was unable to maintain altitude and made a forced landing to a busy highway, during which time the engine lost total power. After the airplane touched down on the highway it impacted a guardrail resulting in substantial damage to the airframe. Examination of the airplane’s fuel system revealed the main fuel tank was intact and empty of fuel and about 3.5 gallons of fuel was drained from the aft tank. The fuel system was configured so that the aft fuel tank gravity fed to the forward tank through the cockpit fuel selector valve. The forward tank fed directly to the engine without flowing through the fuel selector valve. Therefore, when the fuel selector valve was placed to the ON position, it allowed fuel to flow from the aft tank to the forward tank by gravity. The inside of the main tank, which was located between the cockpit and engine firewall, was visually inspected with a flashlight, and no obvious anomalies were noted. The fuel finger screen was clean. Fuel was added to the tank to check for leaks. A considerable fuel leak was immediately observed at the lower left-hand seam of the tank. Blue fuel stains were also observed around the area of the leak. Examination of the rest of the fuel system revealed no anomalies that would have precluded normal operation.