On December 21, 2006, approximately 1555 mountain standard time, a Cavalier F51D Mustang airplane, N251RM, sustained substantial damage following a loss of power and forced landing near the Rexburg-Madison County Airport (RXE), Rexburg, Idaho. The airplane was registered to a private individual. The certificated commercial pilot, sole occupant of the airplane, sustained minor injuries. Visual meteorological conditions prevailed for the local maintenance test flight, which was operated in accordance with 14 CFR Part 91, and a flight plan was not filed. The flight departed RXE about 1520. In a telephone interview with the NTSB investigator-in-charge, and according to the Pilot/Operator Aircraft Accident/Incident Report (NTSB Form 6120.1), the pilot reported that the maintenance test flight was being conducted as a result of a recent engine change. The pilot stated that after departing RXE he over flew the airport area for about 20 to 25 minutes. The pilot further stated that after returning to the airport he completed 2 touch-and-go landings to Runway 35, and was going around for the third [touch-and-go landing] when the engine quit about 300 to 400 feet above ground level (agl). The pilot revealed that after the engine resumed operation he turned to the west, thinking that he could fly a "tight [traffic] pattern" and get the airplane back to the airport. The pilot reported that the engine quit a second time and restarted, "...[but] by then I knew I couldn't make the runway, and the only option I had left was the divided highway (Highway 20)." The pilot stated that as both the northbound and southbound lanes of the highway were busy, he headed for the highway median. The pilot further stated that he thought the left wing stalled about 20 to 30 feet agl, which resulted in the airplane cartwheeling after the wing impacted the ground. The airplane came to rest inverted in the median, and there was no post-crash fire. The pilot reported that there were no mechanical deficiencies with the airplane prior to the flight. A Federal Aviation Administration aviation safety inspector, who traveled to the accident site, reported that the propeller was torn from the engine, the engine was ripped from the firewall, and all engine accessories were destroyed, which prevented further investigation. It was also reported that the airplane had sustained substantial damage to both wings and the landing gear support structure. The reason for the reported partial loss of engine power was not determined.