Idaho Efficient Vehicle Demonstration Act of 2009 - Prohibits any reduction of the apportionment of federal-aid highway funds to Idaho if: (1) it permits a commercial combination vehicle weighing up to 129,000 pounds to operate on specified routes of the Interstate System within the state; (2) such vehicle does not exceed state weight limits for operation on state highways; and (3) the vehicle is limited to travel only on certain portions of Interstate Routes 15, 84, and 86.

(Under current law, the federal-aid highway funds of a state shall be reduced if it permits a commercial combination vehicle with a weight in excess of federal weight limits to operate on Interstate System highways within the state.)