The provisions of this subchapter shall apply only to bridges over navigable waters of the United States, the construction of which is approved after August 2, 1946, under the provisions of this subchapter; and the provisions of the first proviso of section 401 of this title, and the provisions of sections 491 to 494 and 495 to 498 of this title, shall not apply to such bridges.
(Aug. 2, 1946, ch. 753, title V, §507,