***This report was modified on August 7, 2012. Please see the dcoket for this accident to view the original report.*** The pilot reported that, about 2 hours into a visual flight rules cross-country flight, he enriched the mixture due to indications of excessive cylinder head and exhaust gas temperatures. This resulted in a higher fuel burn than planned, so he changed the flight’s destination to a closer airport. While en route to his amended destination, he encountered instrument meteorological conditions. A subsequent buildup of ice resulted in a loss of 100 knots of airspeed as the airplane entered a controlled descent. The pilot executed a 180-degree turn and broke out of the clouds over a valley. During the next 50 minutes, he made several attempts to exit the valley; however, mountain peak obscuration and a thunderstorm prevented him from flying out of the valley. Now very close to fuel exhaustion, he elected to land on a two-lane highway. During the landing roll, the airplane veered off the side of the road, impacted a tree, slid backwards through a ditch, and collided with a concrete drainage culvert. The airplane sustained damage to the outboard sections of both wings.