The pilot reported that during a cross-country flight conducted under instrument flight rules, he encountered clouds that contained clear ice. Ice built up rapidly on the airplane, which was in cruise flight at 16,000 feet. In an effort to get out of the icing conditions, he requested and received clearance to progressively lower altitudes down to 10,000 feet. The airplane continued to accumulate ice. He requested a turn, and this was denied by the controller as there were two other airplanes in the vicinity with similar icing problems. He then requested and received clearance to descend to 9,000 feet, where he could see portions of the ground. At this point, "both windshields were completely covered with clear ice as were the unprotected portions of the aircraft" and both engines were operating at full power. The pilot informed the controller that he needed to descend further. At an altitude of 7,500 feet, he circled several times attempting to see if he could reach an airport for landing. No ice had melted or come off the airplane, and the weather was deteriorating. The pilot decided to land on a highway. On final approach to land, the airplane collided with a power line, which severed the upper half of the rudder and vertical stabilizer. The pilot turned the airplane slightly left, and landed the airplane with the landing gear down in a terraced field next to the highway. During the landing roll, the landing gear was sheared off when the airplane encountered a ditch. The pilot stated that he had "no forward visibility due to the clear ice that completely covered the windshields."