The pilot of the Robinson R-22 helicopter stated that upon reaching cruising altitude, he reached to pull the trim adjustment knob, but inadvertently pulled the mixture control knob, which caused the engine to shutdown. The pilot immediately lowered the collective lever and entered an autorotation. He attempted to restart the engine, using the throttle and the starter, but did not advance the mixture control from the idle cut off position. As he flared the helicopter to land, the windscreen contacted powerlines, and then the helicopter struck an automobile on a roadway. The helicopter sustained damage to the windscreen, main rotor blades, and tailboom. The pilot operating handbook for the Robinson R-22 helicopter states that "If the mixture control is inadvertently pulled in flight, engine stoppage will result. To avoid pulling the wrong control, always reach around left side of cyclic to actuate lateral trim."