Neb. Rev. Stat. § 77-3139

(1) A taxpayer shall claim the tax credit under the Nebraska Shortline Rail Modernization Act by attaching the tax credit certification received from the department under section 77-3138 to its tax return. (2) Any amount of the credit that is unused may be carried forward and applied against the taxpayer's tax liability for the next five taxable years immediately following the taxable year in which the credit was first allowed.