Tolls may be charged for the passage or transit over the Golden Gate Bridge of Government traffic, of military or naval personnel and their dependents, and of civilian employees of the Army and Navy traveling on Government business, but such tolls shall not be in excess of the tolls charged for the passage or transit of other like traffic over such bridge: Provided, however, That subject to the provisions of section 1003 of this title, military and naval personnel, and civilian employees of the Army and Navy, when such personnel or employees are engaged in the performance of official duties requiring the use of such bridge, together with the conveyances being used by them in the performance of such duties, shall have the use of such bridge free of toll.