On January 14, 2002, about 1450 Pacific standard time, a Piper PA-28-180, N3624R, collided with a vehicle during a forced landing on Highway 120 near Groveland, California. The forced landing was precipitated by imminent fuel exhaustion. The airplane was operated by the owner/pilot under the provisions of 14 CFR Part 91. The private pilot received serious injuries; the airplane was substantially damaged. Visual meteorological conditions prevailed at the departure point for the personal flight, and no flight plan had been filed. The flight originated at Truckee, California, about 0945, and was destined for Tulare, California. When the pilot arrived in the Tulare area he was confronted with a low stratus cloud condition. He diverted to Pine Mountain Lake, California, and landed. He contacted an operator at the Tulare airport, who told him that there were visual flight operations there, with cloud bases about 1,500 to 2,000 feet. The pilot departed Pine Mountain Lake and proceeded towards Tulare. Unable to descend through or maneuver around the stratus, he returned to Pine Mountain Lake, which was now covered by the stratus deck, as were other local airports. Realizing he was now too low on fuel to reach an airport in visual conditions, he contacted Oakland Air Traffic Control Center and requested assistance. The center provided vectors towards airports, but due to the weather conditions, the pilot was unable to find the airports. The consensus was to land the airplane as soon as possible and before fuel exhaustion. The pilot spotted a forestry camp with a windsock near Highway 120, about 4 miles east of Groveland. He was successful in landing on the highway; however, the highway had a curve that prevented him from seeing an on-coming vehicle. He attempted to avoid the vehicle but the wing tip clipped it, causing him to lose control and collide with trees.