The provisions of this subchapter shall apply only to bridges over navigable waters of the United States, the construction of which is approved after , under the provisions of this subchapter; and the provisions of the first proviso of , and the provisions of sections 491 to 494 and 495 to 498 of this title, shall not apply to such bridges.section 401 of this titleAugust 2, 19461946-08-02