The Congestion Mitigation and Air Quality Improvement Program Assessing 10 Years of Experience -- Special Report 264 (2002) / Chapter Skim
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Chapter 2 - Context of the CMAQ Program
Chapter 2 - Context of the CMAQ Program
Pages 37-84
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From page 37... ...
The chapter begins with a brief overview of the air quality problem in the United States, its effect on human health and the environment, the contribution of transportation to the problem, the costs imposed by motor vehicle pollution, and the regulatory and planning process for pollution control. Within this broader context, the specific role of the CMAQ program in helping meet air quality standards is addressed.
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From page 38... ...
Another category of pollutants, known as hazardous air pollutants or air toxics, is also regulated under the Clean Air Act. Air toxics are emitted from thousands of sources, such as electric utilities, auto mobiles, and dry cleaners.
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. Health and Environmental Effects of Criteria Pollutants and Air Toxics Concentrations of criteria pollutants that exceed regulated levels are believed to contribute significantly to adverse health effects, which can range from illness to premature death.
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The Health Effects Institute, a nonprofit independent research institute that addresses the health effects of air pollution caused by motor vehi cles, has also conducted several major reviews and reanalyses of a number of key studies (HEI Perspective 2001) , and the American Lung Association has published a review of recent peer-reviewed studies on the health effects of PM air pollution (ALA 2000)
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For 6NOx emissions from motor vehicles, the primary focus of this report, consist of a mixture of NO and NO2 (TRB 1995, 44)
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. In 1999, the most recent year for which data are available, emis sions from transportation sources, also known as mobile source emissions, contributed to more than half (53 percent)
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Pollutant Source Category CO NOx VOCs PM10 Lead SO2 Total Transportation Total 75.1 14.1 8.5 0.8 0.5 1.3 100.3 Highway vehicle share 49.9 8.6 5.3 0.3 0.02 0.4 64.5 Fuel combustion 5.3 10.0 0.9 1.0 0.5 16.1 33.8 Industrial processes 7.6 0.9 8.0 1.3 3.2 1.5 22.5 Miscellaneous 9.4 0.3 0.7 20.6a 0.0 0.01 31.0 Total 97.4 25.3 18.1 23.7 4.2 18.9 187.6 Share of total (percent) All transportation 77.0 56.0 47.0 3.0 12.0 7.0 53.0 Highway vehicles 51.0 34.0 29.0 1.3 0.5 2.1 34.0 Note: CO = carbon monoxide; VOCs = volatile organic compounds; NOx = oxides of nitrogen; PM10 = particulate matter (with mean aerodynamic diameter less than 10 micrometers)
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0660-03/CH02 6/12/02 3:59 PM Page 44 44 the cmaq program: Assessing 10 Years of Experience CARBON MONOXIDE VOLATILE ORGANIC COMPOUNDS 5322 716 9378 904 7590 3232 25162 7996 49989 5297 PM2.5 LEAD PM10 515 766 1029 1263 501 295 22 913 458 4454 229 3162 20634 411 OXIDES OF NITROGEN SULFUR DIOXIDE 320 936 363 5515 1465 10026 942 8590 16091 STATIONARY INDUSTRIAL ON-ROAD NONROAD OTHER Figure 2-1 Sources of criteria air pollutants. Estimated total annual emissions of criteria pollutants from stationary sources, industrial processes, transportation (on-road and nonroad)
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. Including dust from paved roads and sec ondary ammonium nitrate from NOx emissions, motor vehicles may contribute as much as 50 to 75 percent of the fine PM in Denver and Los Angeles.
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Similar to emissions of NOx, SO2 emissions from motor vehicles react in the atmosphere to form sulfate aerosols and hence are an important precursor to PM2.5 (EPA 2001a, 61)
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MOBILE5 and PART5 estimates of 1999 emissions from the on-road motor vehicle fleet. It is likely that MOBILE5 underestimates gasoline VOC and diesel NOx emissions.
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However, far fewer studies have focused specifically on the health costs of motor vehicle emissions.11 Estimating health costs requires a complex set of steps: estimating emissions related to motor vehicle use; estimating changes in expo sure to air pollution; relating these changes to changes in physi cal health effects; and finally relating those effects to changes in 10See the California Air Resources Board website (www.arb.ca.gov) for more informa tion on California's approach to diesel PM emissions.
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. Regulation of Mobile Source Emissions Requirements of the 1990 Clean Air Act Amendments13 As noted earlier, in 1990 Congress enacted a series of amendments to the Clean Air Act to intensify air pollution control efforts across the nation and overhaul planning provisions in those areas that did not meet the NAAQS.
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to demonstrate that transportation plans, programs, and projects would not cause or con tribute to any new violations of air quality standards, increase the fre quency or severity of existing violations, or delay timely attainment of the NAAQS (FHWA 1997, 2)
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The mobile source emissions budget included in an SIP represents the highest level (or ceiling) of emissions allowed from all projects included in local-area transportation plans in a state.15 At the local level, MPOs are responsible for demonstrating that transportation plans and programs conform to the emissions budgets in the SIP.16 The Intermodal Surface Transportation Efficiency Act (ISTEA)
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From page 52... ...
On the other hand, areas that have an NOx prob lem may not choose traffic flow improvements, at least not those that would significantly increase vehicle speeds, which would in turn increase NOx emissions. Of course, CMAQ is not the only revenue source for dealing with local transportation strategies to improve air quality.
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From page 53... ...
Estimating the emission benefits of TCMs and other CMAQ-eligible projects requires the use of models or model inputs whose results are highly uncertain. Pollutant emissions from highway vehicles are currently estimated using a mobile source emission factor model, such as the MOBILE and PART5 models developed by EPA and the motor vehicle emission inventory (MVEI)
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From page 54... ...
A key attribute of congested travel is delay, which is often charac terized as either recurring or nonrecurring. Recurring delay refers to the reduced driving speeds and resulting delays that typically occur each day during peak travel times.
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Costs of Congestion The two primary costs of congestion are vehicle operating costs and the value of travel time. Valuing vehicle operating costs -- primarily fuel costs -- is relatively straightforward.
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23The TTI approach assumes arbitrarily that congestion exists when average daily traffic per lane exceeds 15,000 vehicles on freeways and expressways and 5,500 vehi cles on principal arterial streets. The percentage of daily travel in uncongested condi tions varies by urban area, but the length of the peak travel period is held constant at 50 percent of the average daily VMT for all urban areas (Schrank and Lomax 2001, Appendix B)
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Yet while these critiques 24For example, FHWA has developed a measure of congestion on urban Interstate highways on the basis of traffic volume information and roadway capacity for sam pled sections of highway. Unfortunately, numerous changes in the calculation of highway capacity preclude meaningful trend analysis.
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provides two indicators of congestion derived from estimates of travel delay due to the extra time spent in congested traffic.25 Both indicators compare travel times in peak periods with those in free-flow conditions; one index is based solely on recurring delay, and the other includes both recurring and nonrecurring delay.26 Many urban areas exhibit sub stantial levels of congestion as measured by one or both indicators. The trend data show that between 1982 and 1999, 47 of the 68 urban areas studied suffered a growing time penalty from traffic volume increases and incidents.
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. Of course, air qual ity is determined by more than vehicle emissions; meteorology and topography play important roles, as previously discussed.
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extent that motor vehicle emissions contribute to poor air quality, however, congested travel plays a role. Tailpipe emission rates and thus air quality are linked to conges tion in a complex way.
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Vehicle emissions are lowest in moderate speed ranges, at which vehicle speeds are more uniform and traffic is moving smoothly. At higher speeds, emission levels again rise, reflect ing engine load from aerodynamic drag and high-speed accelera tions from merging maneuvers on freeways, as well as lane-changing and passing behavior on both freeways and high-speed arterial roads (TRB 1995, 116)
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provide a way of adjust ing vehicle emissions for the effects caused by differences in engine performance and driving behavior, including average speeds, aggressive driving (i.e., with sharp accelerations) , and driving on different highway facilities (Brzezinski et al.
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Industry data suggest that diesel PM exhaust emissions fol low the same trend as VOCs up to average speeds of about 50 mph (80 km/h) ; PM10 emission levels at higher speeds are not well understood (TRB 1995, 92)
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However, congestion relief projects must be selected carefully to ensure that traffic speeds do not become so high that emission levels again increase. Contribution of CMAQ to Congestion Mitigation CMAQ Projects and Congestion Relief The CMAQ legislation and regulations clearly prohibit projects that expand highway capacity for single-occupant vehicle (SOV)
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Finally, although a TABLE 2-4 Examples of CMAQ-Eligible Projects That Provide Congestion Relief and Their Effects Effects on Type of Trip CMAQ-Eligible Project Type Congestion Affected Traffic flow improvements Direct Traffic signalization Recurring delays All trips Intersection improvements Recurring delays All trips ITS measures Recurring delays All trips Traffic management centers Recurring delays All trips HOV lanes Recurring delays Work trips Shared ride Direct Carpool and vanpool programs Recurring delays Work trips Related parking programs Recurring delays Work trips Demand management Direct Trip reduction measures Recurring delays Work trips Flexible work hours Recurring delays Work trips Traffic flow improvements Direct Traffic management centers Nonrecurring delays All trips Incident management programs Nonrecurring delays All trips Transit projects Indirect, recurring delays All trips Bicycle and pedestrian projects Indirect, recurring delays All trips Note: ITS = intelligent transportation systems; HOV = high-occupancy vehicle.
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From page 66... ...
Induced Traffic In assessing the final outcome of projects aimed at relieving conges tion, an important complication is the need to account for resulting changes in travel behavior. As travel times are improved on a facility, it is natural for travelers and potential travelers to adjust to the facili ty's increased attractiveness.
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From page 67... ...
The net change brought about by such simulta neous adjustments on the facility in question is called induced travel, induced traffic, or induced demand.34 It is common for evaluations conducted during project planning to account for some but not all sources of induced traffic. Conventional 34Some analysts restrict the term "induced travel" to change resulting from move ment along a short-run demand curve, and use the term "induced demand" to repre sent long-run changes resulting from a shift in that short-run demand curve (Lee et al.
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From page 68... ...
For air quality analysis, it is especially critical to distinguish between shifts that do or do not generate new motor vehicle traffic, although shifts of traffic from other locations or times of day, even if they do not change total trips, VMT, or emissions, can also affect air quality. For congestion relief analysis, it is critical to know whether induced traffic occurs as a result of diversion from other congested facilities.
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A large literature has been produced by those attempting to meas ure the size of induced travel effects.37 While there is ongoing debate over the details, the empirical evidence suggests that these effects are significant and need to be incorporated in any complete assess ment of the results of congestion relief measures. Future Program Direction The context within which the CMAQ program operates has changed since the legislation was enacted in 1991 and is likely to continue to do so.
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From page 70... ...
Current research is focused on characterizing the chemical and physical nature of fine particle emissions and their transformation in the atmosphere, and the levels and chemi cal composition of exposure in the general population and in specific microenvironments (HEI 1999) .40 Work is also under way to link atmospheric concentrations of fine particles to their sources, with particular emphasis on the contribution of exhaust from diesel vehicles.41 Although tailpipe emissions from highway vehicles represent a small share of directly emitted PM on a national basis, they account for a substantially higher proportion of longer-lived atmospheric concentrations of fine particles in urban areas, for example, up to 40 to 50 percent in the Denver and Los Angeles metropolitan areas, as previously noted.
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have been fully implemented in 2009, exhaust emission standards for CO, VOCs, and NOx will be 42Primary emissions from motor vehicles and other combustion sources are highly complex mixtures containing many hundreds of organic and inorganic constituents of gaseous and solid material. Hazardous air pollutants in gaseous state include benzene, 1,3-butadiene, and formaldehyde; volatile and semivolatile organic compounds that are precursors to ozone; organic aerosols; and other hazardous secondary air pollut ants, such as formaldehyde, acetaldehyde, and nitrated polycyclic aromatic hydrocar bons.
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vehicle exhaust emission standards are already 95, 97, and 85 per cent lower, respectively, than precontrol emission rates (see Table 2-5)
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Regarding the first of these, results from dynamic testing of exhaust emissions from properly functioning vehicles show that modern, low mileage vehicles have low CO, VOC, and PM emission rates during the second phase of the test, which represents relatively nonaggres sive driving and fully warmed-up vehicles.46 Emission rates are sub stantially higher for properly functioning vehicles starting cold47 and during intermittent high-engine-load conditions induced by hard 46Running exhaust emissions from the second test phase include emissions from the tailpipe or through the crankcase after the vehicle is warmed up and in a stabilized mode. Exhaust emission rates are determined from dynamometer tests using the Federal Test Procedures (FTP)
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In the past, travel growth appears to have offset some of the projected gains from stricter vehicle emission standards (TRB 1995, 16) .50 The question thus arises of whether metropolitan travel growth and related 48Remote sensing refers to a method for measuring pollution levels in a vehicle's exhaust while the vehicle is in use.
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From page 75... ...
. More flexible work policies and electronic advances that enable work ing at home or from a nearby telecommuting center may also limit work trips and peak-period travel, although there is some evidence that telecommuting can result in an increase in non-commute-related per sonal vehicle trips (Koenig et al.
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From page 76... ...
Advances in Analytic Methods for Estimating Strategy Effects Estimating the pollution reduction potential of many CMAQ-eligible strategies may become easier in the future as new measurement tools become available and more appropriate models are developed. For example, although it may never be possible to measure changes in concentrations of important regional pollutants, such as ozone and PM, due to a particular project, methods for measuring changes in vehicle emissions at the tailpipe and human exposure levels are being developed.
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Conclusions and Implications for Program Evaluation Transportation is one of the many sources of poor air quality in the United States. The primary goal of the CMAQ program is to reduce pollution from motor vehicles.
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For example, projects to provide new capacity for SOV travel, such as the addition of general-purpose lanes to an existing facility or a new highway at a new location, are ineligible even if those projects could help alleviate congestion. The reason for this is that such projects are viewed as not supporting the CMAQ program's primary goal of reducing motor vehicle emissions because they encourage vehicular travel.
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References Abbreviations ALA American Lung Association BTS Bureau of Transportation Statistics EPA U.S. Environmental Protection Agency FHWA Federal Highway Administration FTA Federal Transit Administration HEI Health Effects Institute NCHRP National Cooperative Highway Research Program NRC National Research Council
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1993. An Analysis of High Emitting Vehicles in the On-Road Motor Vehicle Fleet.
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1997b. National Ambient Air Quality Standards for Particulate Matter.
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2001. Exposure Assessment of Air Pollutants: A Review on Spatial Heterogeneity and Indoor/Outdoor/Personal Exposure to Suspended Partic ulate Matter, Nitrogen Dioxide and Ozone.
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1995. On the Costs of Air Pollution from Motor Vehicles.
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2000. Motor Vehicle Facts and Figures 2000.
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