SUMMARY OF MAJOR FEDERAL REGISTER NOTICES PUBLISHED SINCE ENACTMENT OF THE CLEAN AIR ACT AMENDMENTS OF 1990 TITLE II 56 FR 9754 March 7, 1991 40 CFR Part 86 Control of Air Pollution from New Motor Vehicles and New Motor Vehicle Engines: Gaseous and Particulate Emission Regulations for 1994 and Later Model Year Light-Duty Vehicles and Light-Duty Trucks; Proposed Rule Action: Notice of Proposed Rulemaking (NPRM). Today's notice proposes new gaseous and particulate tailpipe emission standards, referred to as the Tier 1 standards, for use in certifying new light-duty vehicles and light-duty trucks. Included are new standards for currently regulated pollutants (carbon monoxide, nitrogen oxides, and particulate matter), as well as the addition of hydrocarbon standards determined on a nonmethane basis. In general, the new standards are functions of vehicle class, weight class, engine cycle (diesel or Otto), fuel, and useful life. New intermediate and full useful life levels, as well as new weight classes are defined. Both petroleum and methanol- fueled vehicles are affected by the proposal. The new standards are implemented in phases, beginning with the 1994 model year. In addition, for the first time, separate in-use tailpipe emission standards and useful life levels are proposed for light-duty vehicles and light-duty trucks. Many aspects of the Tier 1 certification standards apply to the new in-use standards as well, including a phase-in schedule beginning with the 1994 model year, new weight class definitions, and promulgation of both intermediate- and full-life standards. With minor exceptions, which are identified in the proposal, both the Tier 1 and in-use standards are mandated by the 1990 Clean Air Act Amendments (CAAA), and EPA is afforded no discretion in the setting of these standards. Accompanying the Tier 1 and in-use standards are a limited number of proposals to amend the measurement techniques associated with the emission standards. ______________________________________________________________________ 56 FR 31154 July 9, 1991 Proposed Guidelines for Oxygenated Gasoline Credit Programs Under Section 211(m) of the Clean Air Act as Amended Action: Notice of proposed guidelines. Section 211(m) of the Clean Air Act (CAA) as amended by the 1990 Clean Air Act Amendments (CAAA) requires that various States submit revisions to the State Implementation Plans (SIPs), and implement an oxygenated gasoline program. This requirement applies to all States with carbon monoxide (CO) nonattainment areas with design values of 9.5 parts per million or more based on 1988 and 1989 data. The oxygenated gasoline program must require gasoline in the specified control area to contain no less than 2.7 percent oxygen by weight, during that portion of the year in which the areas are prone to high ambient concentrations of carbon monoxide. Section 211(m)(5) requires that EPA promulgate guidelines for State credit programs, allowing the use of marketable oxygen credits for gasolines with higher oxygen than required to offset the sale or use of gasoline with a lower oxygen content than required. Today's notice contains EPA's proposed guidelines for such oxygenated gasoline credit programs. ______________________________________________________________________ 56 FR 31176 July 9, 1991 40 CFR Part 80 Regulation of Fuels and Fuel Additives: Standards for Reformulated Gasoline Action: Notice of Proposed Rulemaking. EPA proposes, in today's notice, two related programs implementing section 211(k) of the Clean Air Act as amended in 1990 by Public Law 101-549. The primary program under that section requires that gasoline sold in the nine worst ozone nonattainment areas be reformulated to reduce toxic and ozone-forming volatile organic compound emissions. The second program prohibits gasoline sold in the rest of the United States from becoming more polluting. These regulations will take effect on January 1, 1995. ______________________________________________________________________ 56 FR 32533 July 17, 1991 40 CFR Parts 80 and 86 Regulations of Fuels and Fuel Additives; Standards for Highway Diesel Fuel Quality-Sulfur Content; and Control of Air Pollution from New Motor Vehicles and New Motor Vehicle Engines: Standards for Oxides of Nitrogen Emissions from Heavy-Duty Diesel Engines Action: Notice of Proposed Rulemaking (NPRM). This notice contains EPA's proposed revisions to 40 CFR part 80 pursuant to section 211(i) of the Clean Air Act (CAA) as amended in 1990. The specific revision presented by this NPRM for part 80 is the requirement that all highway diesel fuels comply with the maximum sulfur content standard of 0.05 percent by weight, effective October 1, 1993. In addition to the preceding statutory required revision, EPA proposes to carry over the existing heavy-duty diesel engine (HDDE) NOx standard of 5.0 g/BHP-hr to the 1994 through 1997 model years, and to correct a typographical error for the viscosity specification for Type 2-D diesel fuel contained in 40 CFR part 86. _______________________________________________________________________ 57 FR 408 January 6, 1992 Clean Air Act; 1990 Amendments Action: Notice of availability. The Environmental Protection Agency has completed the final report on the "Nonroad Engine and Vehicle Emission Study." This study was mandated in the 1990 Amendments to the Clean Air Act and is to be used in determining potential regulation of nonroad engines and vehicles. ______________________________________________________________________ 57 FR 13220 April 15, 1992 40 CFR Parts 80, 86, and 600 Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines; Refueling Emission Regulations for Gasoline-Fueled Light-Duty Vehicles and Trucks and Heavy-Duty Vehicles Action: Final Agency Action Pursuant to Section 202(a)(6) of the Clean Air Act Regarding Onboard Control of Refueling Emissions On August 19, 1987 (52 FR 31162), EPA published a proposal to require vehicle-based (onboard) control of refueling emissions from gasoline-powered light-duty vehicles, light-duty trucks, and heavy- duty vehicles. This notice announces EPA's decision not to promulgate onboard control requirements at this time and explains the rationale for that decision. ______________________________________________________________________ 57 FR 13168 April 15, 1992 40 CFR Part 79 Fuels and Fuel Additives Registration Regulations Action: Notice of Proposed Rulemaking (NPRM) This notice presents proposed regulations for the registration of motor vehicle fuels and fuel additives as authorized by sections 211(b)(2) and 211(e) of the Clean Air Act (CAA). Under the proposed regulations, producers of motor vehicle fuels and fuel additives would be required to conduct certain tests and submit information regarding the composition of emissions produced by such fuels and fuel additives, their effects on the public health and welfare. Additional provisions for determining the effects of fuels and additives on the performance of vehicular emission control devices would be coordinated with existing and future rules under section 211(f). The proposal includes a grouping system and other mechanisms designed to avoid duplicative efforts and reduce the costs of testing by producers of fuels and fuel additives. The proposed regulations would supplement existing registration requirements, and would potentially apply to both current and future fuels and additives. The proposed new requirements are designed to provide a body of information that would assist EPA in evaluating the potential adverse effects of various types of fuels and fuel additives and in determining whether further risk assessment or regulatory action is needed under section 211(c). ______________________________________________________________________ 57 FR 13416 April 16, 1992 40 CFR Part 80 Regulation of Fuels and Fuel Additives: Standards for Reformulated and Conventional Gasoline Action: Supplemental Notice of Proposed Rulemaking This Supplemental Notice of Proposed Rulemaking (SNPRM) describes the standards and enforcement scheme for both reformulated gasoline and for conventional gasoline sold in other areas. It also includes specific proposals for the emission models to be used in gasoline certification and enforcement. The SNPRM reflects a consensus that was reached through regulatory negotiation regarding certain provisions of the reformulated gasoline program. The preamble reflects the basis and purpose of this proposed rulemaking. A copy of the proposed regulatory language discussed herein may be obtained from Public Docket No. A-91-02 or from the contacts in the ADDRESSES section and is deemed to be part of this document. ______________________________________________________________________ 57 FR 31888 July 17, 1992 40 CFR Part 86 Control of Air Pollution from New Motor Vehicles and New Motor Vehicle Engines; Interim Regulations for Cold Temperature Carbon Monoxide Emissions from 1994 and Later Model Year Gasoline-Fueled Light-Duty Vehicles and Light-Duty Trucks Action: Final Rule This final rule establishes cold temperature carbon monoxide (CO) exhaust emission standards for light-duty vehicles (LDVs) and light-duty trucks (LDTs). The emission standards at 20°F, applicable for a 50,000 mile useful life will be: 10.0 g/mi for LDVs; 10.0 g/mi for LDTs with 3,750 lbs or less loaded vehicle weight (LVW); and 12.5 g/mi for LDTs with a LVW greater than 3,750 lbs. These standards will be phased in over a period of three years. In 1994, 40% of each manufacturer's sales volume of LDVs and LDTs will be required to meet the cold CO standards. This percentage increases to 80% and 100% in 1995 and 1996, respectively. Vehicles produced by small-volume manufacturers (less than 10,000 units/year) are exempt until 1996 when 100 percent of these vehicles must comply. Motor vehicle CO emissions continue to contribute to unacceptable CO air quality, with many urban areas exceeding the eight hour CO national ambient air quality standard (NAAQS). In recognition of this persistent problem, the Clean Air Act Amendments of 1990 (CAAA) mandate cold temperature CO control of LDVs and LDTs. This rule will address the mandate of the CAAA and assist noncompliant areas in meeting the CO NAAQS. Mobile source CO emissions will be reduced an estimated 20-29% when measured at 20°F. Averaging over all temperatures, it is estimated that this rule will reduce annual CO emissions by 2.6 - 3.1 million tons by the year 2000 and 5.8 - 7.7 million tons after complete fleet turnover. ______________________________________________________________________ 57 FR 52912 November 5, 1992 40 CFR Parts 85, 86 and 600 Standards for Emissions From Natural Gas-Fueled, and Liquefied Petroleum Gas-Fueled Motor Vehicles and Motor Vehicle Engines, and Certification Procedures for Aftermarket Conversion Hardware Action: Notice of proposed rulemaking. This notice proposes low- and high-altitude emission standards and test procedures for the certification of natural gas-fueled and liquefied petroleum gas-fueled light-duty vehicles, light-duty trucks, heavy-duty engines and vehicles, and motorcycles. The standards are proposed to be effective beginning with the 1994 model year, although vehicles may be certified to the standards in earlier years if the manufacturer desires. This notice also proposes fuel economy test procedures and calculations for natural gas-fueled light-duty vehicles and light-duty trucks to be effective beginning with the 1993 model year. These procedures and calculations will allow natural gas-fueled vehicles to be included in the Corporate Average Fuel Economy (CAFE) program. These standards are being proposed in order to remove the possibility that the absence of such standards could hinder the development of natural gas and liquefied petroleum gas as transportation fuels. These proposed standards are intended to provide a comparable degree of environmental protection to that afforded by the standards applicable to gasoline, diesel and methanol vehicles. In addition to emission standards for gaseous-fueled vehicles, this action proposes requirements for the certification of aftermarket conversion equipment intended to allow a vehicle or engine to operate completely or in part on a fuel other than the fuel for which it was originally designed and manufactured. These proposed requirements are not specific to gaseous fuels, but are proposed to apply to all conversions regardless of fuel type. ______________________________________________________________________ 58 FR 3994 January 12, 1993 40 CFR Part 86 Control of Air Pollution from New Motor Vehicles and New Motor Vehicle Engines; Regulations for Light-Duty Vehicle and Light-Duty Truck 1994, 1995, and 1996 Model Year Durability Testing Procedures, and 1994 and Later Model Year Allowable Maintenance Action: Final rule. This action revises durability procedures and allowable maintenance provisions in the Federal motor vehicle emission certification regulations. The durability program revisions apply to model year 1994, 1995, and 1996 light-duty vehicles (LDVs) and light-duty trucks (LDTs). The rule includes durability procedures for the certification of vehicles subject to the Tier 1 emission standards promulgated on June 5, 1991. The revised durability procedures are in large part consistent with those adopted by the State of California. The allowable maintenance provisions apply to model year 1994 and later LDVs and LDTs. The new regulations generally extend maintenance intervals for LDVs in response to the longer Tier 1 definition of LDV useful life and update the provisions applicable to LDTs. ______________________________________________________________________ 58 FR 9468 February 19, 1993 40 CFR Part 86 Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines; Regulations Requiring On-Board Diagnostic Systems on 1994 and Later Model Year Light-Duty Vehicles and Light-Duty Trucks Action: Final Rule This final rule establishes requirements for on-board diagnostic (OBD) systems on light-duty vehicles and light-duty trucks beginning with the 1994 model year. Section 202(m) of the Clean Air Act (CAA) requires EPA to promulgate rules mandating OBD systems on such vehicles. This rulemaking requires manufacturers to install OBD systems which; monitor emission control components for any malfunction or deterioration causing exceedances of emission standards, and alert the vehicle operator to the need for repair. This rulemaking also requires that when a malfunction occurs, diagnostic information must be stored in the vehicle's computer to assist the mechanic in diagnosis and repair. This rulemaking does not contain the final requirements under which information necessary to perform repair and maintenance service on on-board diagnostic systems and other emission-related vehicle components would be made available to the service and repair industry. Such requirements will be contained in a forthcoming Agency rulemaking. ______________________________________________________________________ 58 FR 11722 February 26, 1993 40 CFR Part 80 Regulation of Fuels and Fuel Additives: Standards for Reformulated Gasoline; Proposed Rule Action: Notice of Proposed Rulemaking This notice proposes revisions to the simple model and the contents of a complex model to be used in the certification of reformulated gasoline, and associated procedures to assure compliance with the reformulated gasoline and antidumping programs. This notice additionally proposes "Phase II" reformulated gasoline emission performance standards which will take effect in the year 2000, as prescribed by section 211(k)(3) and authorized by section 211(c) of the Clean Air Act (CAA). The detailed proposed regulations described herein may be obtained from Public Docket No. A-92-12 or from the contacts listed in the ADDRESSES section. ______________________________________________________________________ March 17, 1993 40 CFR Part 80 Volatility Regulations for Gasoline and Alcohol Blends Action: Final Rule This action revises the gasoline and alcohol blend volatility regulations promulgated on March 22, 1989 and June 11, 1990. The revisions are based on the experience the Agency has gained enforcing these regulations, suggestions from the regulated industry and other interested parties received prior to the NPRM, and comments submitted in response to the NPRM. The revisions include changes to the liability provisions, including amendments to the defenses to liability, the addition of a test exemption section to allow the use of high volatility gasoline during the control period for research or emissions certification, and changes to the Appendix D sampling procedures and the Appendix E tests for determining Reid Vapor Pressure. Changes to EPA's volatility regulations due to the Clean Air Act Amendments of 1990 (Pub. L. No. 101-549) have been addressed in a separate rulemaking promulgated on December 12, 1991. ______________________________________________________________________ 56 FR 50196 40 CFR Part 88 Clean Fuel Fleet Credit Programs, Transportation Control Measure Exemptions, and Related Provisions ACTION: Final Rule. Provisions of the Clean Air Act Amendments enacted in 1990 require the establishment of a Clean Fuel Fleet Program to reduce emissions of ozone precursors, especially non-methane organic gases and oxides of nitrogen, through the introduction of lower-polluting vehicles in specified areas. Under this program, some of the new vehicles purchased by certain fleet owners located in covered areas (certain ozone and carbon monoxide nonattainment areas) will be required to meet clean-fuel fleet vehicle (CFFV) exhaust emission standards. As a part of this program, the Clean Air Act (CAA) requires EPA to promulgate provisions governing state implementation plans (SIPs) that implement a program to grant credits for fleet owners for exceeding purchase requirements and to exempt clean-fuel fleet vehicles from certain transportation control measures (TCMs). Proposed regulations governing the states' implementation of the credit program and TCM exemptions were published on October 3, 1991 (56 FR 50196) and are finalized by today's action. The credit program, which is based on additional emission reductions, allows fleet owners to earn purchase credits from early or extra purchases of CFFVs or by acquiring vehicles which are certified to stricter emission standards than required. A fleet owner may bank credits earned to demonstrate compliance with the purchase requirement at a later date, or may trade them to another fleet. This program will assist the fleet industry in meeting the air quality improvement goals of the fleet program in the most cost-effective manner possible. This action also requires that states provide exemptions from temporally-based TCMs, established wholly or partially for air quality reasons, to all clean-fuel fleet vehicles. The TCM exemptions granted to CFFVs are intended to serve as an incentive to fleets participating in the program to exceed their purchases beyond the requirements. In addition, this rule establishes provisions for a new subgroup of CFFVs, known as inherently low-emission vehicles (ILEVs). This federal program, which is voluntary for both the vehicle manufacturers and the fleet industry, will grant expanded TCM exemptions to vehicles in this group in recognition of their superior emission characteristics. Initially, ILEVs will receive exemptions from high-occupancy vehicle (HOV) lane restrictions; EPA will propose additional exemptions/incentives later this year. These exemptions are intended to provide further incentives to fleet owners to purchase cleaner vehicles than otherwise required by the statute. EPA previously proposed provisions implementing the federal facility provisions of section 246(g) of the Act. EPA has decided to finalize this action by guidance instead of regulation. ______________________________________________________________________ FR 58 15781 March 24, 1993 40 CFR Part 86 Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines; Particulate Emission Regulations for 1993 Model Year Buses, Particulate Emission Regulations for 1994 and Later Model Year Urban Buses, Test Procedures for Urban Buses, and Oxides of Nitrogen Emission Regulations for 1998 and Later Model Year Heavy-Duty Engines Action: Final Rule. This final rule implements several provisions of the Clean Air Act, as amended in 1990, related to buses and heavy-duty engines (HDEs). First, for model year 1993, EPA expands the applicability of the 0.10 gram per brake horsepower-hour (g/bhp-hr) particulate matter (PM) standard currently required of urban bus engines to a broader group of HDEs used in other types of buses. Second, for model year 1994 and 1995 HDEs used in urban buses, EPA promulgates a PM standard of 0.07 g/bhp-hr. (For model year 1996 and later HDEs used in urban buses, the certification and SEA standard is lowered to 0.05 g/bhp-hr, the in-use standard remains at 0.07 g/bhp-hr.) Third, EPA retains the current heavy-duty transient test procedure for emissions testing of urban bus engines. Fourth, in addition to the bus requirements listed above, this final rule also promulgates an oxides of nitrogen (NOx) standard of 4.0 g/bhp-hr for all 1998 and later model year HDEs. Finally, for the two new emission standards promulgated in this action (1994 urban bus PM standard and 1998 HDE NOx standard), the useful life is extended from eight years to ten years. ______________________________________________________________________ FR 58 16002 March 24, 1993 40 CFR Parts 80 and 86 Control of Air Pollution From New Motor Vehicles and New Motor Vehicle Engines: Evaporative Emission Regulations for Gasoline- and Methanol-Fueled Light-Duty Vehicles, Light-Duty Trucks and Heavy- Duty Vehicles Action: Final rule. This action promulgates requirements for revised test procedures intended to reduce evaporative emissions from motor vehicles as authorized by the 1990 amendments to the Clean Air Act and the Act's general standard-setting provisions. Proposals for revised test procedures were published on August 19, 1987 (52 FR 31274) and on January 19, 1990 (55 FR 1914). Since then EPA has held two public workshops, announced December 3, 1990 (55 FR 49914) and December 17, 1991 (56 FR 65461), for further discussion of available test procedure options. The revised test procedures are scheduled for implementation beginning with the 1996 model year, with phase-in completed in the 1999 model year. This action will result in significant reductions of volatile organic compound emissions. Such emissions are a major contributor to the nation's ground-level ozone problem, which is responsible for harm to human health and public welfare. This action also limits fuel pump dispensing rates. Effective January 1, 1996 for most facilities, dispensing rates for gasoline and methanol pumps may not exceed 10 gallons (37.9 liters) per minute. For facilities with low sales volumes, implementation is delayed for two years. This action will ensure that vehicles designed to prevent spitback during refueling will not experience in-use fueling rates beyond the design basis rate. ______________________________________________________________________ FR 58 21359 4/21/93 40 CFR Parts 85 and 86 Retrofit/Rebuild Requirements for 1993 and Earlier Model Year Urban Buses; Fuel Quality Regulations for Certification Diesel Test Fuel Action: Final Rule. This final rule establishes the provisions for an urban bus retrofit/rebuild program as required by section 219(d) of the Clean Air Act Amendments (CAAA) of 1990. The program affects 1993 and earlier model year (MY) urban buses whose engines are rebuilt or replaced after January 1, 1995. The program is limited to urban buses operating in metropolitan areas with 1980 populations of 750,000 or more. Operators of urban buses in the affected areas may choose between two options. Option 1 sets particulate matter (PM) emissions requirements for each urban bus in an operator's fleet whose engine is rebuilt or replaced. Option 2 is a fleet averaging program that requires an operator to meet a specified annual target level for the average PM emissions level from the 1993 and earlier MY urban buses in the operator's fleet. The target levels for an individual operator's fleet are based on the age and engine model distribution of the urban buses in the operator's fleet. The retrofit/rebuild program is intended to reduce the ambient levels of particulate matter in urban areas. This action is also correcting errors in the sulfur content, cetane number, and cetane index specifications for heavy-duty engine certification diesel test fuel. The corrections contained in this final rule were brought to EPA's attention by interested parties. ----------------------------------------------------------------- May 17, 1993 FR 58 28809 40 CFR Part 89 Control of Air Pollution from New Nonroad Mobile Source Engines; Determination of Significance for Nonroad Sources and Emission Standards for Emission of Oxides of Nitrogen and Smoke from New Nonroad Compression-Ignition Engines At or Above 50 Horsepower ACTION: Notice of Proposed Rulemaking. Section 213 of the Clean Air Act (CAA) as amended by the Clean Air Act Amendments of 1990 (CAAA) requires the Environmental Protection Agency (EPA) to conduct a study to determine whether emissions of carbon monoxide (CO), oxides of nitrogen (NOx), and volatile organic compounds (VOCs) from nonroad engines and vehicles contribute significantly to levels of ambient ozone and CO in more than one area not in compliance with the National Ambient Air Quality Standards (NAAQS) for these pollutants. In today's action, EPA is proposing to find that emissions from such nonroad sources significantly contribute to nonattainment of the NAAQS for ozone and CO in more than one area. If The Agency makes this positive determination, section 213 requires EPA to promulgate regulations that will result in reductions in emissions from nonroad sources. Consequently, EPA is proposing in this notice standards for NOx and smoke emissions from nonroad compression-ignition engines greater than or equal to 50 horsepower (hp) (37.3 kilowatts (kw)), with exclusions for certain types of engines. A NOx standard of 6.9 grams per brake horsepower-hour (9.2 grams per kilowatt-hour) and smoke opacity standards of 20% on acceleration mode, 15% on lug mode, and 50% peak opacity in either acceleration or lug mode are proposed. The proposed standards are expected to result in a 37% reduction of NOx from these engines and an average 4.7% reduction in current summertime NOx inventories in ozone nonattainment areas. EPA is also proposing that these engines meet the smoke standards that currently apply to on-highway engines. The proposed standards would be phased-in by horsepower subcategories beginning with the 1996 model year. At this time, EPA is not proposing standards for emissions of hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM) because available test procedures have not been demonstrated capable of predicting emissions of these pollutants from nonroad engines. Further, EPA is not proposing emission standards for other nonroad emission sources in this rulemaking as additional analysis of options, feasibility, and cost-effectiveness is still necessary. Today's notice contains a detailed description of the basis, purpose, and substance of this proposed rulemaking. In an effort to conserve monetary and material resources, EPA has not included in this notice the proposed regulatory language. To obtain a copy of the proposed regulatory language, see the Supplementary Information section below. -------------------------------------------------------------------------- June 10, 1993 FR 58 32474 40 CFR Part 88 Clean Fuel Fleet Emission Standards, Conversions, and General Provisions and Amended Heavy-Duty Averaging, Banking, and Trading Credit Accounting Regulations ACTION: Notice of Proposed Rulemaking (NPRM) Provisions in the Clean Air Act Amendments (CAAA) enacted in 1990 require the establishment of a Clean Fuel Fleet Program. Under this program, a percentage of the new vehicles acquired by certain fleet owners located in covered areas will be required to meet clean-fuel fleet vehicle (CFFV) emission standards. This requirement can be met by the purchase of new CFFVs, the conversion of conventional vehicles to CFFVs, or through purchases of credits pursuant to a credit program. Affected states will be required to revise their State Implementation Plans to incorporate the fleet program, including provisions to implement a credit program and exempt CFFVs from certain transportation control measures (TCMs). The CAAA require EPA to promulgate regulations governing these provisions. Accordingly, regulations were promulgated for the credit program and TCM exemptions. Today's NPRM contains proposals for implementing the additional statutory requirements, which include emission standards for CFFVs and regulations governing the conversion of conventional vehicles to CFFVs. Several key definitions applicable to the Clean Fuel Fleet Program as a whole are also proposed. Separate from the provisions proposed in today's NPRM for the CFF program, EPA is also proposing to change the credit accounting method used in its averaging, banking and trading program for heavy-duty engines such that manufacturers will be allowed to use credits scheduled to expire in the earliest model year before using credits that would expire in later model years.