((a)) ** Standards for model years after 1993** Not later than , the Administrator shall promulgate regulations under applicable to urban buses for the model year 1994 and thereafter. Such standards shall be based on the best technology that can reasonably be anticipated to be available at the time such measures are to be implemented, taking costs, safety, energy, lead time, and other relevant factors into account. Such regulations shall require that such urban buses comply with the provisions of subsection (b) of this section (and subsection (c) of this subsection, if applicable) in addition to compliance with the standards applicable under for heavy-duty vehicles of the same type and model year.section 7521(a) of this title1section 7521(a) of this titleJanuary 1, 19921992-01-01

((b)) ** PM standard**

((1)) ** 50 percent reduction** The standards under applicable to urban buses shall require that, effective for the model year 1994 and thereafter, emissions of particulate matter (PM) from urban buses shall not exceed 50 percent of the emissions of particulate matter (PM) allowed under the emission standard applicable under as of , for particulate matter (PM) in the case of heavy-duty diesel vehicles and engines manufactured in the model year 1994.section 7521(a) of this titlesection 7521(a) of this titleNovember 15, 19901990-11-15

((2)) ** Revised reduction** The Administrator shall increase the level of emissions of particulate matter allowed under the standard referred to in paragraph (1) if the Administrator determines that the 50 percent reduction referred to in paragraph (1) is not technologically achievable, taking into account durability, costs, lead time, safety, and other relevant factors. The Administrator may not increase such level of emissions above 70 percent of the emissions of particulate matter (PM) allowed under the emission standard applicable under as of , for particulate matter (PM) in the case of heavy-duty diesel vehicles and engines manufactured in the model year 1994.section 7521(a) of this titleNovember 15, 19901990-11-15

((3)) ** Determination as part of rule** As part of the rulemaking under subsection (a), the Administrator shall make a determination as to whether the 50 percent reduction referred to in paragraph (1) is technologically achievable, taking into account durability, costs, lead time, safety, and other relevant factors.

((c)) ** Low-polluting fuel requirement**

((1)) ** Annual testing** Beginning with model year 1994 buses, the Administrator shall conduct annual tests of a representative sample of operating urban buses subject to the particulate matter (PM) standard applicable pursuant to subsection (b) to determine whether such buses comply with such standard in use over their full useful life.

((2)) ** Promulgation of additional low-polluting fuel requirement**

((A)) If the Administrator determines, based on the testing under paragraph (1), that urban buses subject to the particulate matter (PM) standard applicable pursuant to subsection (b) do not comply with such standard in use over their full useful life, he shall revise the standards applicable to such buses to require (in addition to compliance with the PM standard applicable pursuant to subsection (b)) that all new urban buses purchased or placed into service by owners or operators of urban buses in all metropolitan statistical areas or consolidated metropolitan statistical areas with a 1980 population of 750,000 or more shall be capable of operating, and shall be exclusively operated, on low-polluting fuels. The Administrator shall establish the pass-fail rate for purposes of testing under this subparagraph.

((B)) The Administrator shall promulgate a schedule phasing in any low-polluting fuel requirement established pursuant to this paragraph to an increasing percentage of new urban buses purchased or placed into service in each of the first 5 model years commencing 3 years after the determination under subparagraph (A). Under such schedule 100 percent of new urban buses placed into service in the fifth model year commencing 3 years after the determination under subparagraph (A) shall comply with the low-polluting fuel requirement established pursuant to this paragraph.

((C)) The Administrator may extend the requirements of this paragraph to metropolitan statistical areas or consolidated metropolitan statistical areas with a 1980 population of less than 750,000, if the Administrator determines that a significant benefit to public health could be expected to result from such extension.

((d)) ** Retrofit requirements** Not later than 12 months after , the Administrator shall promulgate regulations under requiring that urban buses which—

((1)) are operating in areas referred to in subparagraph (A) of subsection (c)(2) (or subparagraph (C) of subsection (c)(2) if the Administrator has taken action under that subparagraph);

((2)) were not subject to standards in effect under the regulations under subsection (a) of this section; and

((3)) have their engines replaced or rebuilt after ,

((e)) ** Procedures for administration and enforcement** The Administrator shall establish, within 18 months after , and in accordance with , procedures for the administration and enforcement of standards for buses subject to standards under this section, testing procedures, sampling protocols, in-use compliance requirements, and criteria governing evaluation of buses. Procedures for testing (including, but not limited to, certification testing) shall reflect actual operating conditions.section 7525(h) of this titleNovember 15, 19901990-11-15

((f)) ** Definitions** For purposes of this section—

((1)) ** Urban bus** The term “urban bus” has the meaning provided under regulations of the Administrator promulgated under .section 7521(a) of this title

((2)) ** Low-polluting fuel** The term “low-polluting fuel” means methanol, ethanol, propane, or natural gas, or any comparably low-polluting fuel. In determining whether a fuel is comparably low-polluting, the Administrator shall consider both the level of emissions of air pollutants from vehicles using the fuel and the contribution of such emissions to ambient levels of air pollutants. For purposes of this paragraph, the term “methanol” includes any fuel which contains at least 85 percent methanol unless the Administrator increases such percentage as he deems appropriate to protect public health and welfare.