The pilot and passenger were reported unhurt and the plane did not hit any vehicles.
Federal Aviation Administration spokesman Allen Kenitzer said in an email that the pilot of the Cessna 182 declared an emergency due to engine failure.
The plane suffered minor damage to its landing gear.
The Washington State Patrol identified the pilot as 63-year-old John Townsley of Spokane. The patrol said the plane was flying from Richland to Spokane when it lost power.
A State Patrol dispatcher in Yakima said one southbound highway lane was blocked late Friday night but traffic was getting by.
The disabled plane was later towed off the freeway to a dirt parking lot. The wings will be removed so the plane can be placed on a trailer and brought to the Tri-Cities Airport for an investigation into what caused the engine to stop.