On August 24, 2021, about 1200 Pacific daylight time, a Piper PA-32-300 airplane, N2843T, was substantially damaged when it was involved in an accident near Del Mar, California. The flight instructor and the pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the airplane had just received an annual inspection, and he was flying it from Montgomery-Gibbs Executive Airport (MYF), San Diego, California, back to McClellan-Palomar Airport (CRQ), Carlsbad, California, its home base. According to the pilot, he did not have a current medical certificate, and the flight instructor was on board to act as pilot in command. They departed from MYF and climbed to about 1,500 ft mean sea level (msl). Once past the class B airspace floor of 1,800 ft msl, the pilot began a slow climb. The engine began to surge, and it sounded like “the throttle was cycling between open and closed.” The airplane began to lose altitude. The flight instructor declared an emergency and turned towards a racetrack. The pilot reported that the auxiliary fuel pump was on, that there were about 60 gallons of fuel on board, and that all electrical power was lost as they descended. The flight instructor and the pilot determined that they could not safely land on the racetrack. Therefore, they elected to land on interstate highway I-5. Spotting a gap between cars, the flight instructor made a forced landing on the interstate. During the landing sequence, the airplane struck several vehicles, which resulted in substantial damage to its wings. The airplane came to rest angled toward the interstate median barrier. A postaccident examination of the airframe and engine revealed that all fuel lines fittings were secured; fuel system continuity was established; and the fuel selector valve operated appropriately. Engine control continuity was established. Rotational continuity of the engine was established through manual rotation of the propeller, and cylinder thumb compression was obtained on all cylinders. During crankshaft rotation, spark was obtained on all ignition leads. All the cylinders were examined with a lighted borescope, which revealed no internal damage and a normal amount of combustion deposits. Overall, the examination revealed no evidence of any pre-impact mechanical failures or malfunctions that would have precluded normal operation. A review of flight data from the engine data monitor revealed that the No. 3 exhaust temperature remained low during the flight. However, the investigation was unable to determine if the exhaust temperature data for the No. 3 cylinder was accurate or the result of a bad sensor. The No. 3 cylinder’s head temperature was similar to those of the other cylinders. The data also revealed that the battery voltage remained constant during the flight. No anomalies that would have precluded normal operation were noted.