The pilot reported that while en route to his planned fuel stop destination, the engine experienced a slight hesitation. The pilot then changed course to the nearest airport and turned on the auxiliary fuel pump. The engine roughness stopped for about 15 seconds, then occurred again, and the engine subsequently lost total power. Unable to maintain altitude and reach the nearest airport, the pilot conducted a forced landing to a roadway. During the forced landing, the airplane’s left wing tip struck a roadway sign, and the right float impacted a moving vehicle that was on the roadway. The airplane sustained substantial damage to the left wing rear spar. Postaccident examination of the airplane revealed the left fuel tank contained no usable fuel, and the right tank contained about 14 gallons of fuel. The fuel selector was found in the left fuel tank position. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.