46 U.S.C. § 53311

A deposited gain, if otherwise taxable income under the law applicable to the taxable year in which the gain was realized, shall be included in gross income for that taxable year, except for purposes of the declared value excess profits tax and the capital stock tax, if— (1) the deposited gain is not expended or obligated within the appropriate period under section 53310 of this title ; (2) the deposited gain is withdrawn before the end of that period; (3) the construction related to that deposited gain has not progressed to the extent of 5 percent of completion within the appropriate period under section 53310 of this title ; or (4) the Secretary of Transportation finds and certifies to the Secretary of the Treasury that, for causes within the control of the taxpayer, the entire construction related to that deposited gain is not completed with reasonable dispatch.