The pilot reported that during the initial climb in night visual meteorological conditions the airplane "was not climbing well." The pilot further reported for about 15 minutes he maneuvered the airplane over a highway, and the airplane still would not gain altitude. Subsequently, he reported that was "unable to maintain adequate terrain separation" and landed on the highway. During the landing roll on the highway, the pilot swerved to avoid a car and struck a road sign, which substantially damaged the left wing. During postaccident correspondence with the pilot, he reported that the airplane was "160 lbs. over gross with high estimates on bags, likely closer to 140 over gross." The Federal Aviation Administration (FAA) Pilot's Handbook of Aeronautical Knowledge (PHAK) in part states: "The pilot should always be aware of the consequences of overloading. An overloaded aircraft may not be able to leave the ground, or if it does become airborne, it may exhibit unexpected and unusually poor flight characteristics. If not properly loaded, the initial indication of poor performance usually takes place during takeoff." The pilot also reported that a cold compression check was performed on the engine after the accident. He reported that the "compressions were 25/80, 42/80, and both rear cylinders were 72/80." The Service Instructions for cylinder compression checks provided by Textron Lycoming in part states: "Operate the engine until normal cylinder head and oil temperatures are attained; then shut down the engine making sure that magneto switches and fuel supply valves are shut off. Proceed with the test as soon as possible after shut down." The cylinder compression measured was not completed in accordance with the manufacture's service instructions. The FAA provides guidance on how density altitude affects aircraft performance. The density altitude about the time of departure was 8,202 feet, the pressure altitude was 6,217 feet, and the temperature was 20 Celsius (68 Fahrenheit). According to the FAA Koch Chart, the airplane would have likely experienced a 145% increase to the "normal takeoff distance" and a 65% decrease in a normal climb rate. The FAA PHAK in part states: "In extreme conditions, such as high gross weight, high density altitude, and high temperature, a deficiency of airspeed during takeoff may permit the aircraft to become airborne but be incapable of sustaining flight out of ground effect." The pilot also reported that he had been on a four day trip and had worked more than 12 hours each day, including the day of the accident. He reported that, "fatigue significantly affected decision making as [the] pilot had opportunities to attempt to land back at [the] airport, abort [the] takeoff, or land closer on [the] highway avoiding the vehicle." The FAA PHAK in part states: "Fatigue is frequently associated with pilot error. Some of the effects of fatigue include degradation of attention and concentration, impaired coordination, and decreased ability to communicate. These factors seriously influence the ability to make effective decisions."