40 CFR 92.305 - Credit generation and use calculation.
(a) For each participating engine family, NOX and PM emission credits (positive or negative) are to be calculated according to the following equation and rounded in accordance with ASTM E29-93a, to the nearest Megagram (Mg). Consistent units are to be used throughout the calculation.
(1) When useful life is expressed in terms of megawatt-hrs:
Credits for each engine family are calculated as: Emission credits = (Std − FEL) × (UL) × (Production) × (Fp) × (10−3 kW-Mg/MW-g).
(i) Std = the applicable locomotive and locomotive engine NOX and/or PM emission standard in grams per kilowatt-hour (exceptions: Std = 0.43 g/kW-hr, for Tier 0 and Tier 1 PM line-haul credits; Std = 0.59 g/kW-hr, for Tier 0 and Tier 1 PM switch credits; and Std = previous FEL in g/kW-hr, for locomotives that were certified to an FEL other than the standard during the previous useful life).
(ii) FEL = the family emission limit for the engine family in grams per kilowatt-hour. For Tier 1 and Tier 2 engine families, the FEL may not exceed the limit established in § 92.304(k) for each pollutant.
(iii) UL = the sales weighted average useful life in megawatt-hours, based on the sales weighted average horsepower of the engine family (or the subset of the engine family for which credits are being calculated), as specified in the application for certification.
(iv) Production = the number of locomotives or locomotive engines participating in the averaging, banking, and trading program within the given engine family during the calendar year (or the number of locomotives or locomotive engines in the subset of the engine family for which credits are being calculated). Quarterly production projections are used for initial certification. Actual applicable production/sales volumes are used for end-of-year compliance determination.
(v) Fp = the proration factor as determined in paragraph (c) of this section.
(b) When useful life is expressed in terms of miles or years, the useful life in terms of megawatt hours (UL) shall be calculated by dividing the useful life in miles by 100,000, and multiplying by the sales weighted average horsepower of the engine family. Credits are calculated using this UL value in the equations of paragraph (a) of this section.
(c) The proration factor is an estimate of the fraction of a locomotive's service life that remains as a function of age.
(1) The locomotive's age is the length of time in years from the date of original manufacture to the date at which the remanufacture (for which credits are being calculated) is completed, rounded to the next higher year.
(2) The proration factors for ages 1 through 32 are specified in Table D 305-1 of this section. For locomotives or locomotive engines more than 32 years old, the proration factor for 32 year old locomotives shall be used.
(3) For replacement or repower engines, the proration factor is based on the age of the locomotive chassis, not the age of the engine.
Table D 305-1 - Proration Factor