All bridges which have heretofore been constructed or rebuilt or which may hereafter be constructed or built over navigable streams by or under the order of the state highways and transportation commission of Missouri, either entirely with state funds or in part with state funds, and local funds, or with local funds or any easement over any privately owned bridge now or hereafter constructed or built in good repair which may be tendered free and without consideration to the state highways and transportation commission, and which bridges are located at points where such streams intersect the state highways, and all bridges now under contract to be erected by the state highways and transportation commission, or in whole or in part from funds of the state highways and transportation commission, shall be regarded as part of the state highways, and all such bridges shall be maintained by the state highways and transportation commission.