On June 30, 2000, approximately 1144 Pacific daylight time, a Piper PA-28-140 airplane, N6887W, was substantially damaged in a forced landing on interstate highway 82 (I-82) approximately 5 miles southwest of Kennewick, Washington. The private pilot-in-command received minor injuries in the accident; a passenger aboard the aircraft was uninjured. The 14 CFR 91 personal flight from Walla Walla, Washington, was en route to an intended destination of Hood River, Oregon at the time of the occurrence. Visual meteorological conditions prevailed, and the flight was on a visual flight rules (VFR) flight plan. The pilot reported that about 30 minutes after takeoff, while cruising at 6,500 feet above mean sea level, the engine started to lose RPM. He stated that he adjusted the mixture and checked fuel pressure, oil pressure and "engine heat" (stating that all were normal), but that the RPM continued to drop and the engine stopped. The pilot stated that he went through his emergency check and found everything normal, then tried to restart the engine. He stated that the engine did restart, but that oil started coming out of the cowling. He reported that to avoid the possibility of an engine fire, he then shut down the engine and turned the fuel pump off. He reported that he called the Walla Walla tower and told them that he had an engine failure, and that he was going to attempt a forced landing, passing his position and setting his transponder to 7700. He stated: I found a road that looked like my best option and began to set the plane up for an emergency landing. The oil was continuing to come out and was covering the windshield obscuring my vision. I was able to land the plane on the road, but had little or no visibility out the front. My left wing hit a road sign, which I could not see, causing the plane to leave the road and come to rest in a ditch beside the road. The pilot supplied copies of the engine logbook indicating that the engine, a Lycoming O-320-E2A, last received an annual inspection signoff on October 17, 1999, at 1,622 hours since overhaul. The pilot reported that the engine had flown 27 hours since this inspection. Textron Lycoming service instructions give the manufacturer's recommended time between overhauls (TBO) of this engine as 2,000 hours. A post-accident disassembly examination of the engine was conducted by Bergstrom Aircraft, Inc., Pasco, Washington, at the request of the NTSB. Bergstrom Aircraft's report of the examination findings (work order number 6424, July 3, 2000, attached) stated that upon removal of the engine's number 1 cylinder, they found piston damage, with the wrist pin brass plug missing. Bergstrom Aircraft also reported a hole in the top of the crankcase, which they stated was "probably caused by [the] brass plug being pushed out by [the] crank shaft lobe."