4
Implementing Emission Controls on Mobile Sources

INTRODUCTION

Since the earliest days of the Clean Air Act (CAA), mobile sources have been recognized as one of the most important sources of air pollution and, as a result, have been a prime target for emission control. Despite almost three decades of increasingly tight and wide-ranging regulations, emissions from mobile sources are still a major source of air pollution in the United States (see Figure 1-2 in Chapter 1). The persistence of the need to address mobile emissions is not, however, an indication that the largely technological controls applied to mobile sources have been ineffective; indeed, emission rates from individual vehicles have decreased substantially since enactment of the CAA. Instead, human behavior and other social factors, such as increases in vehicle miles traveled (VMT) and the growing popularity of sport utility vehicles (SUVs), which had been regulated at a less stringent level, appear to have offset many of the gains achieved from the imposition of technological controls.1 Difficulties in identifying and repairing high-emitting vehicles was probably also a contributing factor.

Currently, a wide variety of mobile sources are subject to control under the CAA. These are broadly divided into on-road and nonroad sources (see Table 4-1). On-road sources include light-duty vehicles (LDVs, also referred to as passenger cars), light-duty trucks (LDTs), heavy-duty vehicles

1  

As discussed later in the chapter, new SUVs will soon be required to meet the same gram-per-mile emission standards as cars.



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Air Quality Management in the United States 4 Implementing Emission Controls on Mobile Sources INTRODUCTION Since the earliest days of the Clean Air Act (CAA), mobile sources have been recognized as one of the most important sources of air pollution and, as a result, have been a prime target for emission control. Despite almost three decades of increasingly tight and wide-ranging regulations, emissions from mobile sources are still a major source of air pollution in the United States (see Figure 1-2 in Chapter 1). The persistence of the need to address mobile emissions is not, however, an indication that the largely technological controls applied to mobile sources have been ineffective; indeed, emission rates from individual vehicles have decreased substantially since enactment of the CAA. Instead, human behavior and other social factors, such as increases in vehicle miles traveled (VMT) and the growing popularity of sport utility vehicles (SUVs), which had been regulated at a less stringent level, appear to have offset many of the gains achieved from the imposition of technological controls.1 Difficulties in identifying and repairing high-emitting vehicles was probably also a contributing factor. Currently, a wide variety of mobile sources are subject to control under the CAA. These are broadly divided into on-road and nonroad sources (see Table 4-1). On-road sources include light-duty vehicles (LDVs, also referred to as passenger cars), light-duty trucks (LDTs), heavy-duty vehicles 1   As discussed later in the chapter, new SUVs will soon be required to meet the same gram-per-mile emission standards as cars.

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Air Quality Management in the United States TABLE 4-1 Types of Vehicles and Engines Regulated by AQM in the United States Source Category Status (Date Promulgated; Effective Date) On-road sources   Light-duty vehicles (LDVs or passenger cars) Tier 2 regulations require about 99% reduction over previous control levels for cars (2000; 2004–2007) Light-duty trucks (LDTs) (pickup trucks, minivans, passenger vans, and sport-utility vehicles with a gross weight of less than 8500 lb) Must comply with Tier 2 Lightest truck (2000; 2004–2007) Heavier light trucks (2000; 2008–2009) Medium-duty passenger vehicles (MDPVs) (vehicles with gross weight 8,500–10,000 used for personal transportation, such as larger sport utility vehicles [SUVs] and passenger vans) Tier 2 standards to be phased in beginning with the 2008 model year (2000; 2008–2009) Heavy-duty vehicles (HDVs) (vehicles with gross weight greater than 8500 lb used commercially, such as large pickups, buses, delivery trucks, recreational vehicles [RVs], and semi-trucks. Highway Heavy-Duty Rule requires new vehicles to meet substantially lower PM and NOx standards (>90% reduction) (2001; 2007–2010) Also strict fuel sulfur levels (15 ppm) (2001; 2006) Motorcycles New standards to reduce emissions by 80% (based on California) (proposed 2002; to take effect 2006–2010) Nonroad Sources   Nonroad, spark ignition (gasoline) engines For handheld engines, new rules require 70% NOx plus hydrocarbon reduction (2000; 2002–2007) New standards promulgated for larger spark ignition engines (2002; 2004–2007) Nonroad recreational vehicles and engines New rules for variety promulgated to require between 55% and 80% reduction in emissions (depending on pollutant) (2002; 2006–2009, depending on type of engine) Nonroad compression ignition (diesel) engines Nine size ranges, including agricultural and construction equipment; existing rules promulgated in 1998 (1998; 1999–2008) New standards comparable to Highway Heavy Duty Rule proposed 2003

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Air Quality Management in the United States Source Category Status (Date Promulgated; Effective Date) Marine engines New recreational engines required to meet new standards with 55–80% reduction in emissions (depending on pollutant) (2002; 2006–2009) Largest maritime commerce engines regulated to international standards for NOx (not PM) (2003; 2004) Smaller maritime commerce engines regulated for NOx, PM (1999) Aircraft Initial standards for smoke only; new standards adopting International Civil Aviation Organization rules requiring 20% reduction in NOx emissions (1997; full effect in 1999) Locomotives Regulations applying to new locomotive engines and to remanufactured engines from 1973 and later locomotives; ultimately (2040) expected to reduce NOx by 60%; PM by 46% (1997; Tier 0 for engines 1973–2001; Tier 1 for engines 2002–2004; Tier 2 for engines 2005 and later) (HDVs), and motorcycles that are used for transportation on the road. On-road vehicles may be fueled with gasoline, diesel fuel, or alternative fuels, such as alcohol or natural gas. Nonroad sources refer to gasoline- and diesel-powered equipment and vehicles operated off-road, ranging in size from small engines used in lawn and garden equipment to locomotive engines and aircraft. In principle, the mobile-source emissions can be controlled with three types of strategies: New-source certification programs that specify emission standards applicable to new vehicles and motors. In-use technological measures and controls, including specifications on fuel properties; vehicle inspection and maintenance programs; and retrofits to existing vehicles. Nontechnological (for example, behavior modification) measures to control usage or activity (for example, via management of transportation). This chapter summarizes how each of those strategies is used in the United States and concludes with a critical discussion.

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Air Quality Management in the United States CONTROLLING EMISSIONS THROUGH CERTIFICATION STANDARDS ON NEW VEHICLES AND MOTORS In the United States, the first mobile-source emission reductions were aimed at lowering the emissions on new vehicles and engines. As older model cars were retired, the in-use fleet would become increasingly populated with regulated vehicles, and emissions would steadily decrease. The first regulations were imposed on passenger cars2 and then were applied to other on-road vehicles, such as trucks and buses, and most recently, to nonroad sources, such as tractors and construction equipment.3,4 The specific emission standards listed in Table 4-1 for mobile-source categories have sometimes been set directly by Congress in an amendment to the CAA, but more typically, the EPA administrator has set such standards. Except for California, states do not have independent authority to set new emission standards (see Box 4-1). At the same time, as standards have been set for vehicle emissions, vehicle manufacturers have also been required to comply with requirements for Corporate Average Fuel Economy (CAFE) standards, which were initiated by Congress in the Energy Policy and Conservation Act of 1975. CAFE established mandatory fuel efficiencies in the form of required miles per gallon (mpg) goals for fleets of passenger cars and light-duty trucks.5 These standards were enacted in the wake of a petroleum supply interruption and were less concerned with air quality improvements. Nevertheless, for a given vehicle technology, reduced fuel consumption per mile would, in principle, result in lower engine-out emissions, and, therefore, result in less burden on the afterengine emission control system to meet a given emission per mile standard. In practice, implementation of the relatively modest CAFE standards appears to have helped in meeting some hydrocarbon emission standards. However, future application of some especially fuel-efficient engines—which have higher engine-out emissions of some pollutants (for example, NOx)—will likely require development of substantially more effective emission control technologies in order to simultaneously improve fuel economy and emissions (NRC 2002c). 2   Although the first federal controls on mobile sources began with regulations on passenger cars for the 1968 model year, California began mandating emission controls on passenger cars in the early 1960s. 3   An exception is aircraft engines, which have been subject to emission regulations since 1974. The earliest regulations were for smoke from turbojet engines. 4   Because nonroad sources have been essentially uncontrolled until recently, their contribution to total mobile-source emissions has grown considerably since passage of the CAA (see Table 4-2). 5   The current CAFE program requires vehicle manufacturers to meet a standard in miles per gallon (mpg) for the fleet they produce each year. The standard is 27.5 mpg for automobiles and 20.7 mpg for light-duty trucks.

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Air Quality Management in the United States BOX 4-1 California’s Unique Role in Controlling Mobile Emissions The CAA expressly precludes any state except California from setting its own motor vehicle emission standards. Because of California’s experience with the most severe air pollution in the nation, it has historically assumed a leadership role in promoting the application of new control technologies for automobiles. By the 1950s, researchers in California had been able to establish a cause and effect linkage between gaseous emissions from motor vehicles and the formation of photochemical smog with its concomitant high concentrations of O3 and PM. In response to that finding, California enacted legislation in 1961 that established statewide new-vehicle emission standards beginning with the 1966 model year. The federal government followed suit in 1965 with the Motor Vehicle Pollution Control Act, which set similar standards for the entire nation beginning with model year 1968. That pattern has been repeated on numerous occasions, as stricter emission standards have been enacted first in California and then propagated to the entire nation by direct congressional mandate or rule-making by the EPA administrator (see Figure 4-1A,B,C). Although states are not allowed to set their own emission standards, the CAA permits them to choose California’s stricter standards (typically as part of their state implementation plans). In addition to emission standards, states can opt for other aspects of California’s more aggressive program to control mobile-source emissions; these include programs on fuel composition, regulation of individual motorists’ use of their automobiles, and controls on transportation infrastructure planning and investment. As a result, California regulations and programs on mobile emissions have played an important role in state implementation plans throughout the nation (see, for example, the discussion on the Ozone Transport Commission in Chapter 3). Emission Standards for Light-Duty Vehicles and Light-Duty Trucks The CAA Amendments of 1970 required auto manufacturers to reduce LDV and LDT emissions by 90%. That reduction was to be achieved for carbon monoxide and hydrocarbon emissions by 1975 and for nitrogen oxides (NOx) emissions by 1976 (Jacoby et al. 1973). However, these standards were not fully implemented until the 1980s. Claiming that the initial compliance dates for a 90% reduction in LDV and LDT emissions were infeasible, the auto industry achieved only a partial implementation of the mandated emission-reduction goals by 1975–1976 (Howitt and Altshuler 1999). The CAA Amendments of 1977, extended the emission standards deadlines for carbon monoxide and hydrogen until 1983 and 1980, respectively. The amendments also extended the deadlines for NOx to 1982 and changed the standard from a 90% to a 75% reduction. In addition, the amendments allowed the EPA administrator to relax the NOx requirement selectively until 1984 for automotive technologies that promised better fuel economy (Crandall et al. 1986).

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Air Quality Management in the United States

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Air Quality Management in the United States FIGURE 4-1 The evolution of California and federal tailpipe standards on passenger car exhaust emissions since the 1960s. (A) NOx emissions, (B) CO emissions, and (C) VOC emissions. NOTE: A, B, and C are not completely consistent. There have been changes in test methods that are accounted for in an approximate manner. Current emission standards for VOC are defined in terms of nonmethane organic gases (NMOG). In addition, the most recent emission standards are based on vehicle categories and an average over these categories. For the California program, manufacturers must meet a fleet average standard for NMOG; for the federal program, manufacturers must meet a fleet average standard for NOx. The “standards” for CO and NOx in California for 1999 and later and the federal standards for NMOG and CO in model years 2004 and later are based on an assumed distribution of standards used for compliance. In addition, vehicles currently have to meet additional useful life standards and standards for supplemental test procedures to test operation under off-cycle driving conditions and under airconditioning operations. Thus, the actual progression of standards has been more stringent than shown in the figure. These figures are for exhaust emissions only. For the uncontrolled vehicles in 1960, there were also VOC emissions from crankcase blowby, which have been completely eliminated, and evaporative VOC emissions, which have also had a high degree of control. Note that the vertical axis on the VOC and NOx charts is a log scale. The federal Tier II standards apply to a full useful life of 120,000 miles. Those standards have been adjusted to equivalent 50,000-mile-useful-life standards using data from CARB, which has standards for both 50,000 and 120,000 miles.

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Air Quality Management in the United States Despite the difficulties and delays in implementation, passage of the emission standards from LDVs and LDTs represented a watershed in AQM in the United States: Congress’s adoption of a “technology-promoting” strategy for lowering mobile-source emissions and, over time, industry’s response by developing and installing new and innovative pollution-control technologies for passenger cars (for example, catalytic converters) (see Box 4-2). As this new technology was developed, refined, and installed on new LDVs and LDTs in the 1980s, the emission characteristics of new vehicles sold in the United States steadily and dramatically improved. As higher-polluting vehicles were replaced by newer ones, emission controls became widespread in the U.S. automotive fleet (Howitt and Altshuler 1999). The catalytic-control technology developed in the United States to meet the emission standards mandated in the CAA is now broadly used throughout the world. In China, for example, all cars operated in the Beijing metropolitan area are required to have catalytic controls either as factory-installed equipment or as a retrofit (Liu et al. 1999; Webb 2001). Despite those technological advances, many areas could not meet the National Ambient Air Quality Standards (NAAQS) for ozone (O3). That was due to challenges in reducing emissions from all sources, but among mobile sources, there was continued growth in VMT and new scientific and technological information that some emissions, especially evaporative emis- BOX 4-2 Technology Innovation and Emission Controls The development and widespread application of pollution-control technologies have permitted reductions in criteria pollutant emissions even while vehicle miles traveled has continually increased. Early pollution-control technologies included positive crankcase ventilation valves to direct crankcase blowby emissions into the engine; charcoal canisters to sequester volatile hydrocarbons for later burning in the engine, exhaust gas recirculation valves to reduce NOx formation during fuel combustion; and catalytic converters designed to oxidize partially combusted hydrocarbons and CO to CO2. Today, vehicles are being driven by cleaner fuels (for example, the removal of fuel sulfur to extend the life of catalytic converters and the further development and improvement of emission-control technologies including high-performance and three-way catalytic converters capable of reducing NOx to nitrogen gas, hydrocarbon adsorbents, coupled engine-exhaust controls that optimize air-to-fuel mixtures, and leak-free exhaust systems). These technologies are also being expanded for use on heavy-duty vehicles and nonroad equipment. The recent introduction of new automotive technologies, such as electric-gasoline hybrid vehicles with lower fuel consumption, will further decrease emission levels. The continued development of new technologies and application of current technologies to unregulated or less stringently regulated sources is expected to continue to drive decreases in criteria pollutant emissions.

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Air Quality Management in the United States sions, were not being fully controlled. In addition, HDVs and nonroad vehicles were important contributors. The CAA Amendments of 1990 mandated emission reductions (referred to as Tier I controls) for LDVs by 1994. In addition to calling for further reductions in NOx and volatile organic compounds (VOCs), the 1990 requirements tightened significantly the controls on evaporative emissions, especially during refueling.6 Also, the 1990 CAA Amendments authorized the EPA administrator to establish more stringent Tier II controls in 2004 if they were judged to be needed, technically feasible, and cost-effective (Howitt and Altshuler 1999). The Tier II regulations have since been promulgated. Besides the tightening of NOx and VOC emission standards, Tier II includes a limit on the sulfur content of fuels (to extend the effective lifetime of catalytic converters) and regulations on medium-duty passenger vehicles (MDPVs), such as the largest SUVs,7 as well as a provision that allows manufacturers to use fleet averaging to meet the NOx standards. The entire set of regulations will be phased in between 2004 and 2009. The CAA authorizes California to set stricter vehicle emission standards because of the magnitude of its air pollution problems. California required manufacturers to achieve average emissions that were lower than those mandated by the federal Tier I regulations, beginning with the 1994 model year. The state also defined a family of low-emissions vehicles: the transitional low-emissions vehicle (TLEV), the low-emissions vehicle (LEV), and the ultra-low-emissions vehicle (ULEV). In addition, California required manufacturers to offer consumers so-called zero-emission vehicles, or ZEVs,8 by 1998 and achieve a 10% statewide market share for ZEVs by 2003 (Sperling 1991). California has delayed and modified its requirement for ZEVs and has recently made additional modifications in response to a June 2002 federal district court injunction that prohibits implementation of 6   An enhanced aspect of the emission standards mandated in the CAA Amendments of 1990 was the inclusion of tighter standards on evaporative emissions as well as the more conventional tailpipe emission standards. The addition of tighter evaporative emission standards was in direct response to research in the late 1980s that pointed to these emissions as an important and growing problem (NRC 1991). 7   The increasing popularity of SUVs has caused an unintended emissions increase because these vehicles had been governed by emission regulations for trucks. The truck regulations are intended to provide for emissions control while allowing the truck to operate under heavy loads. The new Tier 2 regulations define a new class, medium-duty passenger vehicles (MDPV), which must meet the same gram-per-mile emission standards as cars, starting with the 2008 model year. 8   ZEVs are so-called because they are electric-powered cars and as such have no tailpipe emissions. Nevertheless, the name is misleading. If the electricity used to power a ZEV is generated from burning fossil fuel, then its operation will certainly result in pollutant emissions at the power plant.

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Air Quality Management in the United States the 2001 Amendments to the ZEV program for the 2002 and 2003 model years.9 The CAA authorized states other than California to adopt the California standards. After the 1990 CAA Amendments set more stringent requirements for nonattainment areas, Maine, Massachusetts, New York, and Vermont chose to include California mobile emission standards in their state implementation plans (SIPs). In 1994, the Ozone Transport Commission (OTC) (described in Chapter 3) petitioned EPA to impose these automotive technology standards on the entire region, including the states that had not done so individually (Howitt and Altshuler 1999). EPA complied, but their decision was overturned when the District of Columbia circuit court determined that EPA lacked the authority to do so. A series of negotiations among concerned states, automobile manufacturers, environmental groups, and EPA that took place between 1995 and 1998 led to the national low-emission vehicle (NLEV) program. EPA set regulations for this voluntary program; these regulations came into effect only when individual states and automobile manufacturers opted into the program. ZEVs, and the ability of individual states to require them by electing to apply California vehicle standards, were a major issue in these negotiations. Ultimately, Massachusetts, New York, and Vermont retained the requirement for California vehicles, including ZEVs, while the NLEV program was applied in all other states. With the implementation of the Tier II program, the difference in standards between the California program and the federal program will be substantially reduced, one exception being the ZEV mandate in California, Massachusetts, New York, and Vermont. Emission Standards for Heavy-Duty Vehicles LDVs have traditionally been the target of new-vehicle emission standards. However, as emission rates from LDVs declined and the use of on-road freight increased, HDVs became responsible for an increasing fraction of the overall mobile-source emissions of NOx and particulate matter of up to 10 micrometers in diameter (PM10) (EPA 2001a, 2003a). The differentiation between LDVs and HDVs historically has been 8,500 pounds gross vehicle weight (the weight of the vehicle plus the weight of the rated load-hauling capacity). In response to this trend, EPA began regulating HDVs in the 1980s and adopted new-vehicle emission standards at several junctures. 9   The basis of the injunction was not directly related to the emission standards but rather to language in the ZEV requirement that the court found was a form of “fuel economy” mandate that federal law reserves for the federal government alone (Central Valley Chrysler-Plymouth, et al. v California Air Resources Board, et al. E.D. Cal. 2002).

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Air Quality Management in the United States EPA issued new, even more stringent regulations on emissions from HDVs in early 2001 (65 Fed. Reg. 59896 [2000]; 66 Fed. Reg. 1535 [2001]). These new regulations are similar to the Tier 2 standards for LDVs discussed in the previous section in that they require both a tightening of emission certification standards and a decrease in the fuel sulfur content. The regulations, to be phased in between model years 2004 and 2010, will reduce PM and NOx emissions by at least 90% from current standards. To meet these more stringent standards for diesel engines, the sulfur content of diesel fuel will be reduced by 97% from its current level of 500 parts per million (ppm) to 15 ppm beginning in 2006 in most cases. The HDV emission standards are technology-promoting in that they will require the use of new exhaust-after-treatment technologies for diesel-powered HDVs, as well as substantial requirements for control technology life (up to 435,000 miles in some vehicles). In contrast to LDVs, which have included after-treatment technologies (catalytic converters) since the mid-1970s, previous emission standards on HDVs have only required modifications of engine operations. However, meeting the new NOx and PM standards will require diesel-powered HDVs to further refine engine operations, as well as include control technology for NOx and PM. Emission Standards for Nonroad Engines Compared with the long history of regulation of LDV emissions, nonroad mobile-source emissions, like HDV emissions, have been relatively unregulated and, as a result, represent a growing fraction of overall mobile-source emissions (see Table 4-2). In fact, with the set of currently enacted controls, nonroad emissions already exceed on-road emissions of PM and are projected to exceed on-road mobile emissions of VOC and carbon monoxide (CO) in the next two decades. Regulation of these emissions presents some specific challenges to air quality management (AQM). For TABLE 4-2 Contribution of Nonroad Emissions to Mobile-Source Total and to Manmade Total   Nonroad Emissions (1,000s of tons per year), yr Nonroad as a Percent of Mobile-Source Total, yr Nonroad as a Percent of Manmade Total, yr Pollutant 2000 2020 2000 2020 2000 2020 HC 3,488 3,139 47.7 58.0 19.1 20.3 CO 25,843 37,331 34.2 43.3 26.4 34.0 NOx 5,447 4,164 40.6 67.0 22.2 25.7 PM 466 510 66.0 77.9 15.0 16.8   SOURCE: EPA 2002r.

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Air Quality Management in the United States tives (such as road-use tolls and parking surcharges) or to restrict parking at all, and EPA effectively abandoned efforts to enforce the federal TCPs (Altshuler et al. 1979; Howitt and Altshuler 1999). The 1977 CAA Amendments did not mandate restrictions on personal travel, although they permitted states to adopt restrictions if they wished. They also authorized the federal government to withhold most federal highway funds from any state failing to submit an acceptable SIP to EPA (Howitt and Altshuler 1999). Although the states did submit their SIPs, very few proposed or implemented controls on personal travel (Horowitz 1978; Deakin 1978; National Commission on Air Quality 1981; Yuhnke 1991). The CAA 1990 Amendments again left the decision of whether to adopt transportation control measures to state and local officials, with one major exception: mandated employer trip reduction programs (the employee commute options [ECO] requirement) in the 10 most severely polluted nonattainment areas. Some of the 10 affected areas initially proceeded with EPA’s ECO program, requiring employers to reduce the amount of automobile commuting to their work sites. Beginning in 1994, EPA found it difficult to defend the ECO program against growing resistance from business groups because few emission-reduction benefits were expected from the program. Congress made the program voluntary in December 1995 (Public Law 104-70). Outside the United States, there have been a number of efforts to try to address motorist behavior. These include strict restrictions in Singapore (Chia and Phang 2001), alternate day vehicle restrictions in a number of cities, and recent efforts to impose a user fee for drivers into central London. Although these programs may provide some useful insights, some have been implemented in very different governmental circumstances (for example, the authoritarian practices of the Singapore government). Also, others have taken place in the context of broader government policies that have imposed a much higher cost of fuel than is politically realistic in the United States. Still others, such as the London experiment, are not substantially different from programs already in place in the United States. For example, the cost of crossing the Hudson River into New York City is already nearly as high as the new charge imposed in London. Regulatory and other efforts under the CAA to reduce motor vehicle use have proved to be politically infeasible. On the other hand, some efforts to promote voluntary reductions in vehicle use, such as ride-sharing programs, enhancement of existing transit service, compressed work weeks, and telecommuting, have won political acceptance. However, such programs generally have little potential to affect overall use of motor vehicles; each is expected to yield about 1–3% reductions in VMT (Apogee Research 1994; Howitt and Altshuler 1999).

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Air Quality Management in the United States Controls on Transportation Infrastructure Planning and Investment Another class of strategies that can be undertaken to reduce motor-vehicle emissions focuses on optimizing urban and regional transportation patterns and practices. Such strategies require careful integration of urban and regional plans for land use, transportation infrastructure, housing, and economic development. Because they are implemented on decadal time scales, their successful implementation requires a continuing commitment on the part of local and regional managers and politicians to long-term air quality improvement. Within the general theme of transportation planning and AQM, highway capacity has become a highly contentious and complex issue. Because free-flowing traffic at moderate speeds produces less pollution per vehicle mile than highly congested traffic produces, construction of additional highway lanes and access roads would seem to improve air quality. However, highway expansion in a metropolitan area can encourage urban sprawl and low-density development (TRB 1995). Low-density development, which, in turn, increases the number and length of vehicle trips, decreases vehicle occupancy rates, and diminishes the practicality of pedestrian and transit trip making. Similarly, road building to alleviate congestion in densely developed corridors may induce additional travel, because a great deal of latent travel demand in such areas invariably has been suppressed by the existing congestion. The end result can be an increase in automobile travel and increased mobile-source emissions.17 Linking Highway Capacity Expansion to Air Quality through the National Environmental Policy Act In its initial forms, the SIP process lacked a formal procedure to ensure that automobile usage and VMT projections used by air quality planners in NAAQS attainment demonstration were consistent with regional plans for highway and road construction. Before the 1990 CAA Amendments, neither federal law nor the practices of metropolitan transportation planning linked air quality management with urban transportation investment policy. The National Environmental Policy Act (NEPA) of 1969 had attempted to address this problem by mandating that federally funded projects be broadly analyzed for their impacts on the environment. However, NEPA only required that environmental impacts be considered in evaluating projects; it did not provide substantive guidelines for permitting projects to proceed to construction, nor did it require consistency with the projections used in 17   Others argue that the causal factors shaping metropolitan growth and development and associated vehicle usage are more complex than this viewpoint allows (TRB 1995).

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Air Quality Management in the United States SIPs. In addition, NEPA’s project-by-project focus did not generally consider the cumulative environmental effects of multiple projects. Further efforts to create links between air quality regulation and regional transportation planning and investment encountered significant institutional problems and resistance. Section 109(j) of the Federal-Aid Highway Act of 1970 required the secretary of transportation, in consultation with the EPA administrator, to issue regulations for the purpose of ensuring that federally assisted highway projects were consistent with the air quality plans for each pollution control area. However, the regulations were vague on the question of how consistency should be determined, and they had state transportation officials, rather than environmental regulators, making the consistency determinations. In most areas, EPA regional offices made little effort to activate Section 109(j). The 1977 CAA Amendments contained stronger language but were only marginally more effective (Howitt and Altshuler 1999). The Conformity Regulations The CAA Amendments of 1990 and the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 required much tighter integration of (or conformity between) clean air and transportation planning (Howitt and Moore 1999a). The conformity regulations most directly affect metropolitan planning organizations (MPOs), the public agencies that conduct transportation planning under federal transportation law (ISTEA from 1991 to 1997 and TEA-21 [Transportation Equity Act for the 21st Century] since then). Other agencies and stakeholders also play a role. A significant aspect of the conformity regulation is the incentive given to both air quality and transportation planners to maintain conformity. The penalty for non-conformity is a transportation funding cutoff. For some metropolitan areas, that can mean the loss of more than $100 million per year. At the core of the conformity requirement is an EPA-mandated analytical procedure and regulatory test to ensure that transportation-related emissions in a nonattainment area stay within the limits used in the area’s SIP. As described by Howitt and Moore (1999a), the process involves use of a computer simulation to make a 20-year forecast of emissions from the transportation system. The forecast takes into account changes in demographics, land use, economic development, and transportation infrastructure and services. The forecasted emission concentrations are compared with the maximum emissions permissible in certain milestone years under the state’s SIP. If those concentrations exceed permissible levels in the SIP, an MPO must change its transportation plans and programs so that forecasted emissions would be within the emission budget constraints. Alternatively, the state must amend its SIP to reduce transportation-related

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Air Quality Management in the United States emissions through additional mobile-source control measures or reduce emissions from stationary sources, such as industrial facilities or smaller area sources. In addition, an MPO must demonstrate timely implementation of transportation control measures in SIPs and fulfill the ISTEA “fiscal-constraint” requirement for transportation plans and programs by showing that it is likely to have sufficient financial resources to carry them out. If an MPO cannot satisfy the conformity requirements within specified time periods, then penalties are imposed during a conformity “lapse” or “freeze.” During this time, the MPO may not begin most new transportation projects, and the use of federal transportation funds is restricted. Conformity lapses or freezes can also result from certain shortcomings in a SIP, which may or may not involve transportation-related issues (Howitt and Moore 1999a). To date, the most widespread effects of conformity have been procedural and cultural. Before the conformity regulations of the 1990 CAA Amendments, transportation planning and air quality regulation were effectively separate spheres of government activity, even within a given state. Conformity appears to have fostered greater interaction; as a result, it is likely that transportation and environmental agencies have gained more knowledge about and a greater appreciation for one another’s missions, responsibilities, and procedures. Most transportation officials also seem to accept the legitimacy and high priority of environmental values in transportation decision-making (Howitt and Altshuler 1999). Thus far, the conformity requirement has had the largest impact on NAAQS nonattainment areas experiencing rapid growth and, therefore, substantial economic and political pressure to expand transportation infrastructure. Atlanta, Charlotte, and Houston, for example, have had federal transportation funding interrupted because of conformity problems. As further emission reductions are required in the years ahead, nonattainment areas that are rapidly growing are likely to experience conformity as an increasingly salient constraint. It is uncertain how the conflicts between transportation and air quality goals in such areas will be resolved and whether the federal government will remain firm in enforcing the regulation. The conformity requirement has had less impact on transportation planning in older, more slowly growing metropolitan areas. These areas have more mature highway networks and well-established transit systems, and most of their transportation projects, involving highway and transit reconstruction and modest expansions, are neutral or positive in terms of air quality. In addition, these areas often have more serious air pollution problems and thus more time to come into compliance with the CAA (see Table 3-1 in Chapter 3). Therefore, conformity has not required these

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Air Quality Management in the United States areas to make major adaptations. However, these regions have not yet met their stiffest challenges, because they still must demonstrate future reductions in transportation-related emissions (Howitt and Moore 1999b). CRITICAL DISCUSSION OF MOBILE-SOURCE EMISSION-CONTROL PROGRAMS The CAA has led to substantial successes in some aspects of its mobile-source programs. The emissions standards for individual LDVs and HDVs have promoted a host of new technologies, which have resulted in or are expected to result in emissions that are substantially lower than they were in 1970. These emission standards also resulted in eliminating the largest source of lead in the environment through the control of lead in fuels. Despite increasing travel, which has offset some of the gains, the number of communities having air that is not in attainment of the NAAQS for lead or CO (pollutants that are primarily from mobile sources) has dropped dramatically. As described in a recent NRC (2003b) report, that drop has resulted in substantial reductions in overall population exposures to high concentrations of ambient CO. Mobile-source emission-control programs have also experienced and continue to experience challenges, including the persistence of high-emitting gasoline vehicles and older diesel vehicles, the relative lack of regulation of nonroad engine emissions, the contributions of mobile sources to HAP emissions (see discussion of HAPs in Chapter 5), the use of fuel policy to pursue other non-air-quality-related interests (for example, farm policy and reducing dependence on foreign oil), and the inability of AQM to affect individual travel behavior substantially. The following section reviews and summarizes some of the lessons learned and the challenges ahead. Promotion of New Technologies Using Vehicle Emission Standards The history of vehicle emission controls is one of long-term success, albeit success that came more slowly than policy-makers originally intended. Delays were due in part to opposition from the automotive industry facing the challenge of producing the required technologies in a cost-effective manner. Nonetheless, substantial improvements in technology have occurred: more efficient combustion resulting in fewer partially combusted hydrocarbons; emission-control systems with longer effective lifetimes; and the application of many new catalyst and sensor technologies, using increasingly sophisticated computer controls. Actual costs of the improvements have often proved to be less than anticipated (Anderson and Sherwood 2002; Cackette 1998). Lower costs were realized as production

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Air Quality Management in the United States experience was acquired, economies of scale were achieved, and the desire to meet a mass market had fueled substantial competition. Some observers have suggested that such economies are more likely when policies target a relatively small number of large corporations and focus on inducing substantial (but not radical or technologically infeasible) changes in product technology (Howitt and Altshuler 1999). Even so, the process can be marked by considerable controversy and even litigation. Delays are often unavoidable, and accommodations between legislative purposes and industry interests are a frequent part of the implementation process. Nevertheless, the technology promotion process appears to be able to provide the nation with a significant mitigation of air pollution in a cost-effective manner (Howitt and Altshuler 1999). High-Emitting Gasoline Vehicles The emission-control program for mobile sources has been very successful in terms of its ability to reduce emissions from individual LDVs, operated in normal modes. The forecast emission reductions from recently promulgated regulations, if fully effective over the lifetime of an operational vehicle, will provide a further dramatic reduction in mobile-source emissions. However, analyses suggest that historically, a disproportionately large fraction of the mobile emissions come from a relatively small percentage of so-called high-emitting cars. Many of these high emitters are vehicles whose pollution control devices are not operating properly or whose engines are combusting combinations of fuel and lubricating oil. In addition to representing significant sources of VOC, NOx, CO, and air toxics, high-emitting gasoline vehicles might also be significant contributors to ambient concentrations of PM2.5 (Watson et al. 1998). That possibility suggests that attainment of the new NAAQS for PM2.5 will require a much better understanding of the effect of engine operation and deterioration on the emissions of fine particles from gasoline vehicles. The continued presence of high emitters, which were first described by Wayne and Horie (1983) and which continue to be observed in the contemporary vehicle fleet (NRC 2001c and references therein), will reduce the emission reductions that are forecast for programs to be implemented in the latter half of this decade. To date, the nation’s AQM system has not come up with an effective and politically acceptable means to address this problem. One mechanism, which appears to have been at least partially successful, has been to require increasingly durable, warranted emission-control systems, resulting in substantially more robust emission-control systems. New vehicles are currently certified to 100,000 mile standards and major emissions control equipment, such as the catalyst and on-board computer, are warranted for 80,000 miles. Other mechanisms, such as inspection and

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Air Quality Management in the United States maintenance and remote sensing, have been either politically controversial, technically ineffective, or both. A further opportunity, as yet unrealized, might lie in the improvement and monitoring of on-board diagnostic devices that immediately notify drivers of problems and in the long run provide officials and mechanics with accurate information on the performance of emission-control equipment. Reducing Emissions from Older and Nonroad Diesel Engines Although there has been and probably will be substantial progress in reducing the emissions from new on-road diesel vehicles, three substantial challenges remain. First, the long life of diesel vehicles and the pattern in which older vehicles are used for shorter-haul routes in urban centers result in a large and continuing source of PM and NOx diesel emissions in urban settings with dense populations. Recent efforts by the states and EPA to promote buy-back, replacement, and retrofit programs have begun to address this issue, but these efforts have been modest. Second, the recent enforcement experience with on-road emissions being higher than those certified for the engines and the difficulty of inspection and maintenance for heavy-duty engines will require continued attention. Finally, as on-road LDV emissions continue to decline, emissions from various nonroad sources and on-road diesel vehicles will become increasingly important. Recent regulatory efforts by EPA (as detailed above) have begun to address this last issue. Although these recent efforts have begun to address the issue of in-use heavy-duty vehicle emissions, there is not yet a systematic, nationwide approach to the problem. Specific recommendations for addressing this problem are advanced in Chapter 7. Regulating the Content of Gasoline and Diesel Fuels The past 15 years have seen a substantial increase in CAA programs regulating the composition of fuel. In some instances, these programs have been directly responsible for substantial decreases in exposure to important air pollutants—most notably, lead—and for a substantial reduction in benzene emissions and exposure with the advent of RFG. The elimination of sulfur is also likely to facilitate a new generation of gasoline and diesel control technologies, as occurred with the removal of lead in the 1980s. This potential for further technological innovation, however, depends on the successful implementation of the sulfur-reduction regulations on the time scale envisioned in the regulations. The success of these new fuels in reducing key precursors for O3 is less clear. Congressional requirements for oxygen in RFG that resulted in increased use of ethanol may have resulted in increasing evaporative emis-

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Air Quality Management in the United States sions and, in some instances, a worsening of O3 conditions (NRC 1999b). As indicated above, such actions were taken not only for air quality reasons but also for other reasons (for example, farm policy and energy security). The challenge of reducing O3 precursors is made larger by the limitations of the current technical tools available for predicting motor vehicle emissions as a function of the fuel blend (for example, the Simple and Complex models used for RFG). For MTBE, the oxygen requirements also resulted in increasing the risk of groundwater and surface-water contamination (EPA 1999f). One advantage of such programs has been to reduce emissions in older, less well-controlled vehicles. However, many of these older LDVs have now been replaced, but there is no provision for reviewing and, if appropriate, removing specific fuel requirements as the older LDVs are replaced. Finally, Tier II fuel requirements have included banking, averaging, and trading provisions to improve the cost-effectiveness of the rules. To date, however, with the exception of the lead phase-out, there has not been adequate experience to evaluate these programs and to determine their effectiveness. Such evaluation will be especially important as EPA implements the new sulfur-reduction requirements, and extends them to nonroad diesel fuel. Controls on Motorists’ Behaviors In contrast to the success of new motor vehicle standards, efforts to regulate citizen’s personal travel behavior through restrictions or economic disincentives have typically provoked controversy and, in the end, have proved to be politically infeasible. Even where some effort has been made, the estimated pollution reductions have been modest. After 30 years of efforts to affect individual driving behavior, all involved—Congress, EPA, and state and local agencies—have opted to emphasize voluntary versions of such efforts (Howitt and Altshuler 1999). Conformity In the related area of regulation of infrastructure investments, some modest progress appears to have been made. The 1970 and 1977 CAA Amendments were ineffective in ensuring consistency between state transportation investments and air quality improvement commitments. The 1990 CAA Amendments embodied a more realistic appreciation of how transportation decisions can affect air quality planning and backed the requirement for conformity with the tangible threat of federal fiscal penalties for failure to comply. The invigorated “conformity” requirement appears to have enhanced the attention paid to air quality objectives in metro-

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Air Quality Management in the United States politan transportation planning, although it has not, to date, significantly affected state transportation investment decisions. Perhaps the most important substantive effect of conformity may be a new way of looking at highway projects in the early stages of the transportation planning process. Proposals for major highway enhancements, which can be “emission budget busters,” may now be less likely to move into the preliminary planning stage, particularly because planners must show that the financial resources needed to carry out the proposals are likely to be available. Only a few rapidly growing areas have been motivated by conformity requirements to pursue major investments in mass transit, because such investments rarely produce significant air quality benefits. In the areas that already have extensive transit networks, however, the conformity requirements have reinforced the importance of modernization, service enhancements, and occasional extensions (Howitt and Moore 1999b). The relationship between SIP development and the conformity process can create difficulties for both planning and regulatory purposes for several reasons: assumptions, data, and forecasts. These difficulties occur when the two planning processes are insufficiently interconnected. The federal conformity regulations mandate the use of the most up-to-date transportation-planning assumptions and data available (for example, for travel behavior, population, land use, and economic growth) and the most recent version of the emission forecasting models (that is, EPA’s MOBILE model or California’s EMFAC model). Because conformity analyses must be revised at least every 3 years in nonattainment areas and SIPs might not be updated for much longer periods, the underlying assumptions, data, and models used in the transportation-planning process may vary significantly from those in the air quality plan. The disjunction of modeling inputs and methods, depending on the circumstances, can create differences in estimates of future emissions that may only exist on paper in the planning process or mask real air quality problems. Thus, the disconnection between SIP development and the conformity process undermines the intended usefulness of conformity as a performance test allowing informed judgment of whether state transportation investments are consistent with air pollution reduction commitments in the SIP. Moreover, the planning horizons for air quality regulation and transportation planning may mesh poorly. Under current requirements, transportation plans are required to have a 20-year time horizon, and conformity is done on that basis. An attainment demonstration and associated maintenance plan, however, need only a 10-year time horizon. Transportation plans must therefore often use emission budgets that do not take account of future emission growth in transportation and other sectors (Harrington et al. 2003). Both the possible disjunction of planning assumptions and forecasts between SIPs and conformity analyses and the poorly meshing time frames

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Air Quality Management in the United States of the two processes can create important questions about regulatory fairness. The procedures of the CAA were designed so that, in setting emission budgets, decision makers would take forecasts of aggregate emissions and then explicitly allocate emission estimates across sectors in ways that created legitimacy and stakeholder commitment to the outcome. If transportation emission forecasts are updated while other sectors’ are not, the validity and perceived fairness of the results can be questioned and stakeholder support for pollution reductions can be undermined. Some proponents of conformity hoped that linking transportation and land use would encourage broader acceptance of land-use regulations to reduce emissions from mobile sources. However, the impact of conformity on land-use decision-making, which is in the hands of local governments that do not have a direct role in conformity, has been modest (Howitt and Moore 1999a). SUMMARY Strengths of the Mobile-Source Emission-Control Program Regulations on LDVs and LDTs have resulted in significant reductions in the emissions per mile traveled. In the case of CO, as shown in a recent NRC study (NRC 2003b), those reductions have resulted in significant reductions in overall population exposure. Further emission reductions are anticipated from the implementation of stricter emission regulations in the coming years. Emission regulations on LDVs and LDTs have promoted the development and application of new cleaner technologies for vehicles—technologies that are now used worldwide. Furthermore, the actual costs of these technologies were likely less than anticipated. Regulations on fuel properties, including content, have also resulted in air quality benefits, most notably is the phase-out of lead in gasoline that made the use of catalytic converters possible and reduced population exposure to lead. RFG resulted as well in reductions in population exposure to benzene. New regulations on sulfur content in fuels promise to further enhance the effectiveness of catalytic controls and reduce emissions of the on-road fleet. Limitations of the Mobile-Source Emission-Control Program18 Gaps remain in the ability to monitor, predict, and regulate in-use vehicle emissions. The existence of high emitters is a major challenge, and 18   Recommendations are provided in Chapter 7.

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Air Quality Management in the United States I/M programs have been less effective than expected in identifying high emitters and ensuring in-use compliance with emission standards. Other approaches, such as remote sensing and on-board diagnostics, show technical promise, but further testing of those techniques is needed. There is also a concern that remote sensing may be viewed as unacceptably invasive. As emissions from LDVs and LDTs decrease and the focus on attaining the NAAQS for PM2.5 increases, emissions from nonroad engines and heavy-duty onroad vehicles are becoming increasingly important. New emission regulations for these sources are being implemented, but the long lifetime of these engines will slow the rate of penetration of the effects of these regulations into the fleet. Additional efforts in inspection and maintenance and in promoting retrofit and incentive buy-back programs are therefore needed. The inclusion of content-specific requirements in the fuel provisions of the 1990 CAA Amendments (for example, oxygen in the RFG program) can limit flexibility to meet standards in the most cost-effective way for areas required to implement the program. The standards also make it difficult to adjust the program in the face of new challenges (for example, in the case of MTBE contamination of groundwater and surface water) and have a small (sometimes even negative) impact on the control of some air pollutants (as might have been the case with the use of ethanol and potential increases in RVP). Growth in vehicle miles traveled, personal automobile usage, and popularity of fuel-inefficient vehicles (for example, SUVs) has offset a significant portion of the gains obtained from stricter emission standards on individual vehicles. With the exception of the conformity requirements of the 1990 CAA Amendments and subsequent related legislation, air quality managers remain unable to affect these societal and behavioral determinants of mobile-source emissions.