Transportation Conformity Reference Guide
Section D: Specific Regional Analysis Requirements
Chapter 10 PM10 Nonattainment and Maintenance Areas
Modeling Requirements for PM10 Nonattainment and Maintenance Areas
Criteria and Procedures for Determining Conformity for PM10 Nonattainment and Maintenance Areas
PM10 Control Measures
- Paved Road Travel
- Unpaved Road Travel
- Industrial Paved Road Travel
- Construction Site Preparation
- On-road and Non-road Motor Vehicle Exhaust
- PM10 Precursors
- Do serious PM10 areas need to use network models to model PM10 emissions?
- When do PM10 areas need to model construction-related dust?
Exhibit 10-1: Requirements for PM10 Nonattainment & Maintenance Areas
Exhibit 10-2: Potential Transportation Source Control Measure Parameters
In addition to the regional analysis criteria and requirements applied to all areas at all times (as discussed in Chapter 5), and in order to demonstrate conformity, PM10 nonattainment and maintenance areas are required to follow these specific criteria, as stated in the transportation conformity rule,
40 CFR §93.122(d)
In all areas not otherwise subject to paragraph (b) of this section, regional emissions analysis must use those procedures described in paragraph (b) of this section if the use of those procedures has been the previous practice of the MPO. Otherwise, areas not subject to paragraph (b) of this section may estimate regional emissions using any appropriate methods that account for VMT growth by, for example, extrapolating historical VMT or projecting future VMT by considering growth in population and historical growth trends for VMT per person. These methods must also consider future economic activity, transit alternatives, and transportation system policies.
Areas without network models may project vehicle miles traveled (VMT) using any appropriate methods that account for VMT growth by, for example, extrapolating historical VMT or projecting future VMT by considering growth in population and historical growth trends for VMT per person. These methods must also consider future economic activity, transit alternatives, and transportation system policies. All VMT estimates must be "calibrated" to HPMS. Also, all methods related to VMT estimations must be decided through interagency consultation.
40 CFR §93.122(b)(3)
Highway Performance Monitoring Systems (HPMS) estimates of vehicle miles traveled (VMT) shall be considered the primary measure of VMT within the portion of the nonattainment or maintenance area and for the functional classes of roadways included in HPMS, for urban areas which are sampled on a separate urban area basis. For areas with network-based travel models, a factor (or factors) may be developed to reconcile and calibrate the network-based travel model estimates of VMT in the base year of its validation to the HPMS estimates for the same period. These factors may then be applied to the model estimates of future VMT. In this factoring process, consideration will be given to differences between HPMS and network-based travel models, such as differences in the facility coverage of the HPMS and the modeled network description. Locally developed count-based programs and other departures from these procedures are permitted subject to the interagency consultation procedures of §93.105(c)(1)(i).
Modeling Requirements for PM10 Nonattainment and Maintenance Areas
The requirements for regional analysis in PM10 nonattainment and maintenance areas are listed below:
- There are no network-based travel modeling requirements. However, areas already using network-based models must continue to do so, and must follow the six network-based modeling requirements included in 40 CFR §93.122(b)(1)(i)-(vi) and discussed in Chapter 8, and
- All areas not using network-based models are required to use best professional practice to account for VMT estimates, such as HPMS, with the methodology to be determined through the interagency consultation process pursuant to 40 CFR §93.122(d).
Criteria and Procedures for Determining Conformity for PM10 Nonattainment and Maintenance Areas
In addition to the criteria listed in 40 CFR §93.109(b) - Table 1 of the transportation conformity rule, the conformity determination for PM10 nonattainment or maintenance areas is also based on the criteria specific to the nonattainment areas and is summarized in Exhibit 10-1. In order to demonstrate conformity, PM10 nonattainment and maintenance areas need to perform "conformity tests" using their regional emissions analysis. Detailed discussion of these requirements is provided in the transportation conformity rule and in Chapter 5.
PM10 Control Measures
EPA generally interprets the 1990 CAA to require the implementation of increasingly stringent control measures in areas with more serious pollution control problems. Moderate PM10 nonattainment areas are required to identify and select a mix of reasonably available control measures (RACM) needed to assure attainment of the NAAQS. Serious nonattainment areas are required to select a mix of the best available control measures (BACM), thus providing more stringent reductions than RACM. EPA has published guidance on the selection and analysis of PM10 control measures for serious nonattainment areas. It defines BACM as:
59 FR 41998, August 16, 1994
...the maximum degree of emissions reduction of PM10 and PM10 precursors from a source... which is determined on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, to be achievable for such source through the application of production processes and available methods, systems, and techniques for control of each pollutant. For PM10, BACM must be applied to existing source categories in nonattainment areas that cannot attain within the moderate area time frame.
In general, EPA prefers measures that prevent PM10 emissions over the long term versus temporary controls. The former is considered inherently more effective as it eliminates emissions and requires fewer administrative and enforcement resources. EPA believes that BACM requires "a greater emphasis on the merits of the technology alone and less flexibility in considering other factors."
EPA requires BACM SIP revisions to evaluate the technical and economic feasibility of all relevant control measures that reduce the emissions of source categories that are determined to be either above the de minimis level or expected to produce future exceedances.
EPA guidance on technical feasibility for area source control measures is quite limited; however, an assessment of the impact of a selected control measure on one or more of the characteristics that affect emissions from a source is required. These characteristics generally include the following:
- The size or extent of the source (e.g. vehicle-miles traveled on an unpaved surface);
- Physical characteristics (e.g. moisture content of materials handled); and
- Operating practices (e.g. maximum vehicle speeds on unpaved roads).
Guidance on economic feasibility indicates that the capital costs, annualized costs and cost effectiveness of all technologically feasible control measures should be considered. The assessment, however, should not be concerned with the ability of a particular source to "afford" to implement a control measure. Instead, EPA requires "evidence that the control technology has previously been implemented at other sources in a similar source category without unreasonable economic impacts."
EPA PM10 planning guidance defines critical source parameters as source characteristics that affect emissions. Such characteristics include the size or extent of the sources, their physical characteristics, and their operating procedures. A discussion of critical parameters that are essential to the success of any measure aimed at reducing transportation-related PM10 source emissions is presented below.
Paved Road Travel
EPA's emissions factor guidance document, AP-42, lists the emissions factor variables for dust emissions from paved road travel as total dust loading on the road surface and silt content of the dust. The factor governing source size is vehicle-miles traveled on paved roads.
Unpaved Road Travel
AP-42 lists the emissions factor variables for dust emissions from unpaved road travel as silt content of road surface material, vehicle speed, vehicle weight, number of wheels per vehicle, and number of precipitation days per year. The factor governing source size is vehicle-miles traveled on unpaved roads. From an enforcement perspective, it would be very difficult to regulate the weight and number of wheels of vehicles traveling over unpaved roads. As a result, the factors listed above with the exceptions of vehicle weight, number of wheels, and precipitation frequency are deemed to be critical source parameters for unpaved road travel.
Industrial Paved Road Travel
AP-42 lists the emissions factor variables for dust emissions from industrial paved road travel as total dust loading on the road surface and silt content of the dust. The factor governing source size is vehicle-miles traveled on industrial roads. As no significant impediments to the regulation of each of these factors have been identified, all of these factors are concluded to be critical source parameters for industrial paved road travel.
Construction Site Preparation
AP-42 lists the emissions factor variables for construction site preparation as surface silt content and surface moisture content. The factor governing source size is vehicle-miles traveled over the construction site. As no significant impediments to the regulation of each of these factors have been identified, all of these factors are concluded to be critical source parameters for construction site preparation.
On-road and Non-road Motor Vehicle Exhaust
There are a number of factors that contribute to on-road and non-road motor vehicle PM10 exhaust emissions rates. For many of these factors, such as operating mode (i.e., cold start), no practical enforcement approach is available to alter baseline values. For factors relating to source extent, such as vehicle-miles traveled, the suggested control measures consist of travel reduction proposals, which collectively would provide very limited reduction to source extent. As a result, only programs that modify engine design, engine maintenance practices, or fuel specifications appear to hold potential for significantly reducing baseline emissions. Because the significant fraction of motor vehicle PM10 emissions are generated by diesel-powered vehicles, only those control measures that impact this fleet are generally analyzed. Thus, the critical parameters for on-road and non-road motor vehicle exhaust are determined to be engine design (including exhaust controls), engine maintenance practices, and fuel specifications for diesel vehicles.
PM-10 Precursors
The formation of secondary ammonium nitrate can be a source causing significant impacts during the winter season at urban center monitoring sites. A summary of the control measure parameters for the transportation-related source categories discussed above is displayed in Exhibit 10-2. The number of control measures available to influence these parameters is extensive. For this reason the reader is referred to the following documents for additional information on the subject of the control of transportation-related PM10 emissions:
- Controlling Particulate Matter Under the Clean Air Act: A Menu of Options, STAPPA/ALAPCO, July 1996;
- PM-10 Innovative Strategies: A Sourcebook for PM-10 Control Programs, U.S. Environmental Protection Agency, December 1993; and
- Particulate Control Measure Feasibility Study, Maricopa Association of Governments, January 24, 1997.
Questions and Answers
Do serious PM10 areas need to use network models to model PM10 emissions?
In the preamble to the 1993 conformity rule (58 FR 62212, Nov. 24, 1993), EPA specifically discussed whether serious PM10 nonattainment areas should be required to use transportation network models, as required for serious and above ozone and CO areas. EPA decided the network models in PM10 areas are not required because EPA believes that the resources involved in such modeling efforts in PM10 areas may often exceed the benefits. Agencies in PM10 areas must consult with each other on how to model PM10 emissions.
When do PM10 areas need to model construction-related dust?
The procedures for determining regional transportation-related emissions for PM10 from construction-related fugitive dust (See Appendix F) are discussed in the transportation conformity rule as follows:
40 CFR §93.122(e)(1)-(2)
- PM10 from construction-related fugitive dust.
- For areas in which the implementation plan does not identify construction-related fugitive PM10 as a contributor to the nonattainment problem, the fugitive PM10 emissions associated with highway and transit project construction are not required to be considered in the regional emissions analysis; and
- In PM10 nonattainment and maintenance areas with implementation plans which identify construction-related fugitive PM10 as a contributor to the nonattainment problem, the regional PM10 emissions analysis shall consider construction-related fugitive PM10 and shall account for the level of construction activity, the fugitive PM10 control measures in the applicable implementation plan, and the dust-producing capacity of the proposed activities.
