disbursing funds to a city or county under this program shall obtain written assurance from the city or county that the funds shall be expended for purposes of noise mitigation and that the funds shall be spent not later than 2 fiscal years after the disbursement of funds to the city or county. (4) Definitions In this subsection: (A) Noise-affected location The term noise-affected location means any city or county in which ten or more measurements described in paragraph (1)(B) were taken during the previous fiscal year. (B) Noise mitigation The term noise mitigation means soundproofing and noise dampening, including the installation of noise dampening windows, residential noise insulation, and other residential improvements that reduce the impact of noise. (C) Residential building The term residential building means a single family housing unit or a multifamily housing unit. . (b) Revenue diversion exception Section 47107(k) of title 49, United States Code, is amended— (1) by redesignating paragraphs (3) through (5) as paragraphs (4) through (6), respectively