Within one year after termination of employment with DOT, no former DOT employee shall appear personally before DOT on behalf of any person other than the United States in any DOT proceeding or matter in which the United States is a party or has a direct and substantial interest and which was under his or her official responsibility at any time within one year preceding termination of such responsibility. The term “official responsibility” means the direct administrative or operating authority, whether intermediate or final, and either exercisable alone or with others, and either personally or through subordinates, to approve, disapprove, or otherwise direct Government action.