The pilot of the biplane reported that he believed he had departed with 38 gallons of fuel in the main fuel tank and 17 gallons in the auxiliary fuel tank. En route, the auxiliary fuel tank ran dry, so he switched to the main fuel tank, which he believed had a remaining 35 gallons of fuel. The pilot reported that, while descending to the destination airport, the engine experienced a loss of power. He added that he believed the throttle linkage had broken and the carburetor was at idle. During the forced landing, he aligned the airplane with a highway and observed four semi-tractor trailers, but thought they were ahead of his flight path. The airplane struck one of the semi-tractor trailers, violently turned to the right, and came to rest inverted on the right side of the highway. The airplane sustained substantial damage to the left wings. Postaccident examination revealed that the main fuel tank was empty, and the throttle linkage was intact. The pilot reported that his habitual fueling process is to fuel the main fuel tank before fueling the auxiliary fuel tank. He added that he reviewed fuel receipts and discovered that, before the accident flight, he fueled the auxiliary fuel tank first and, while following his routine, believed that the main fuel tank had already been fueled. This resulted in a departure with 10 gallons of fuel less than planned. The pilot reported that there were no preaccident mechanical failures or malfunctions with the biplane that would have precluded normal operation.