; and (11) since the Federal retail excise tax on certain new heavy trucks, tractors, and trailers is based on annual sales, receipts from the tax deposited in the Highway Trust Fund can vary greatly. 3. Repeal of excise tax on heavy trucks and trailers (a) In general Chapter 31 of the Internal Revenue Code of 1986 is amended by striking subchapter C (and by striking the item relating to such subchapter from the table of subchapters for such chapter). (b) Conforming amendments (1) Section 4072(c) of such Code is amended to read as follows: (c) Tires of the type used on highway vehicles (1) In general For purposes of this part, the term tires of the type used on highway vehicles means tires of the type used on— (A) motor vehicles which are highway vehicles, or (B) vehicles of the type used in connection with motor vehicles which are highway vehicles. (2) Exception for mobile machinery (A) In general Such term shall not include tires of a type used exclusively on mobile machinery. (B) Mobile machinery For purposes of subparagraph (A), the term mobile machinery means any vehicle which consists of a chassis— (i) to which there has been permanently mounted (by welding, bolting, riveting, or other means) machinery or equipment to perform a construction, manufacturing, processing, farming, mining, drilling, timbering, or similar operation if the operation of the machinery or equipment is unrelated to transportation on or off the public highways, (ii) which has been specially designed to serve only as a mobile carriage and mount (and a power source, where applicable) for the particular machinery or equipment involved, whether or not such machinery or equipment is in operation, and (iii) which, by reason of such special design, could not, without substantial structural modification, be used as a component of a vehicle designed to perform a function of transporting any load other than that particular machinery or equipment or similar machinery or equipment requiring such a specially designed chassis. . (2) Section 4221 of