In addition to the provisions of N.H. Rev. Stat. § 260:47 and 260:48 any carrier, excepting privately owned school buses, granted a certificate of public convenience and necessity or public interest permit by the commissioner authorizing regularly scheduled transportation service, at least 90 percent of which service, determined in miles, is furnished within the limits of one incorporated city or town in this state and in motor vehicles designed to transport 12 or more passengers, shall be entitled to a refund of road tolls as provided in this subdivision. The refund shall be for an amount representing the percentage, computed on a calendar month basis, which the total miles operated over regularly scheduled routes by the carrier in motor vehicles entirely within the limits of the city or town is of the total miles operated by the carrier throughout its system. The procedure for such refund shall be the same as that provided under N.H. Rev. Stat. § 260:47, III and IV.