Section, added
Pub. L. 91–172, title VII, § 705(a), Dec. 30, 1969,
83 Stat. 672; amended
Pub. L. 94–455, title XVII, § 1702, title XIX, § 1906(b) (13)(A), Oct. 4, 1976,
90 Stat. 1760, 1834;
Pub. L. 95–473, § 2(a)(2)(B), Oct. 17, 1978,
92 Stat. 1464, related to amortization of railroad grading and tunnel bores.