On December 27, 1993, at 1823 eastern standard time, a Piper PA-28-181, N4320X, was substantially damaged following collision with terrain during a forced landing near Greer, South Carolina. The private pilot was not injured in the accident. A passenger in the aircraft received minor injuries. The aircraft was being operated under 14 CFR Part 91 by the pilot. Visual meteorological conditions existed at the time, and an instrument flight rules flight plan was in effect for the flight. The flight departed Baltimore, Maryland for Greenville, South Carolina at 1430 eastern standard time. On approach to Greenville-Spartanburg Airport, the pilot reported to Air Traffic Control (ATC) personnel that the aircraft was low on fuel. ATC offered vectors to a nearby airport, which the pilot initially declined. Shortly thereafter, the pilot requested a diversion to the alternate, which ATC provided. Approximately two miles from the alternate airport, the pilot reported loss of engine power and the intention to perform an emergency landing. ATC advised the pilot of a highway within one mile of his position and the pilot reported the highway in sight. The pilot set up an emergency approach, but soon realized that the airplane was headed into automobile traffic. While attempting a 180 degree turn to avoid landing in oncoming traffic, the airplane crashed into trees off of the highway. The pilot reported that he had calculated 20 minutes of reserve fuel during pre-flight planning. He stated that during the flight, he observed that his actual time enroute was less than he had planned, and he thought he would have enough fuel without a planned fuel stop. He stated that he failed to take into account the use of 75% power during the flight, and the additional fuel burn, as opposed to the 65% power used for his fuel burn calculations during his pre-flight planning.