La. Roads, Bridges and Ferries § 48:881
The exercise of the powers conferred by this Sub-part constitutes the performance of essential governmental functions, and as bridges which are owned and operated by parishes constitute public property used for public purposes, those bridges and the tolls and revenues thereof are free from taxation within the state and no parish shall be required to pay taxes or assessments upon the bridge or any part thereof, owned by it, whether located within or without the corporate limits of the parish. Bonds issued under the provisions of this Sub-part, their transfer, and the income therefrom, including any profits made on the sale thereof, are free from taxation within the state and otherwise as may be allowed by any law.
La. Roads, Bridges and Ferries § 48:881