National Ambient Air Quality Standards. Transportation agencies across the country have a vital role in implementing the laws and regulations established to protect the nation’s air quality. The primary law governing air quality is the Federal Clean Air Act (CAA). The Environmental Protection Agency has set national air quality standards for six principal air pollutants (also referred to as criteria pollutants): carbon monoxide, lead, nitrogen dioxide (NO₂), ozone, particulate matter, and sulfur dioxide. Transportation contributes to four of the six criteria pollutants: carbon monoxide, nitrogen dioxide, ozone, and particulate matter. If monitored levels of any of these pollutants violate the national ambient air quality standards, then the EPA, in cooperation with the State, will designate the contributing area as "nonattainment." Transportation agencies play an important role in setting nonattainment area boundaries, providing essential information on commuting and travel patterns.

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Developing State Implementation Plans. State air, environmental or health agencies are responsible for the development of state implementation plans (SIPs) that explain how the nonattainment area will meet the requirements of the CAA. State and local transportation agencies are required to implement these measures, so it is important that they take an active role in development of the SIP. A SIP is required for each pollutant for which the nonattainment area violates the National Ambient Air Quality Standards. A SIP describes the measures a State will use to bring nonattainment areas into attainment, including public involvement. EPA must approve each SIP, and if a SIP isn't acceptable or the State fails to submit one, EPA must impose sanctions and ultimately assume responsibility for enforcing the Clean Air Act in that State.  Depending on the severity of nonattainment, the CAA requires various transportation-related activities, programs and strategies. States also have the option of choosing among a variety of additional voluntary transportation measures. States are also required to submit a maintenance plan, after they have attained the National Ambient Air Quality STandards, that demonstrates how the State will maintain the standards for 20 years.

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Emissions Inventory. One of the first steps in the development of a SIP is the preparation of an emissions inventory, which is based on the actual or modeled emissions from all sources of air pollution within the nonattainment area. The inventory of mobile source emissions is further categorized by on-road and non-road emissions. The emissions inventory helps define the extent of the pollution problem, relative to the air quality standards in current and future years. The on-road mobile source portion of the inventory should be developed in very close cooperation with State and local transportation agencies. Emission estimates for on-road mobile sources are usually based on the combination of two fundamental measures: vehicle miles of travel (VMT) and emissions rates (the rate of pollutants emitted in the course of travel based on vehicle speed and other factors). The EPA and the U.S. DOT have developed a series of tools and models to estimate the emissions produced by on-road mobile sources. The development of an emissions inventory for on-road mobile sources for an area requires a cooperative effort between air quality agencies and transportation agencies.

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Control Strategies. Once the emissions inventory is completed, including emissions estimates for all sources, air quality modeling or some analytical method may be required to determine the total needed emissions reductions. Once the total emissions reductions target is determined, control strategies must be determined to demonstrate how emissions are to be reduced to that level. Projected changes in population, industrial activity, travel, and other social and economic factors must be evaluated, and control strategies must reflect any projected growth to ensure that emissions are reduced to the actual level needed. The selected measures will be some combination of stationary, area, on-road, and off-road controls. The selected measures result in a certain level of emissions reductions from each source category. This allocation of emissions reductions is intended to allow for States to determine the fastest and most cost-effective way of reaching the level of total emissions estimated to result in attainment.

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Transportation Control Measures. Of the control strategies States may choose to implement, some may be on-road mobile source measures to reduce vehicle use or change traffic flow or congestion conditions. These measures are known as transportation control measures (TCMs). A TCM is any measure that is specifically identified in the SIP for the purpose of reducing emissions or concentrations of air pollutants from transportation sources. The SIP must provide for the implementation and enforcement of TCMs. TCMs should be developed jointly by transportation and air agencies as part of the transportation planning process, and incorporated into the SIP. In addition, many transportation plans and TIPs include TCM-like projects such as transit investments or HOV lanes, which are not included in the SIP. These measures can help improve air quality but are not considered legally enforceable commitments unless they are identified as TCMs in the SIP.

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Motor Vehicle Emissions Budget. The allocation of emissions reductions and control strategies results in an emission reduction target for all sources. For on-road mobile sources, this target can be translated into an area's motor vehicle emissions budget (MVEB), which identifies the allowable on-road emissions levels to attain the air quality standards. These budgets are, in effect, a cap on emissions and represent the "holding capacity" of the area. The motor vehicle emissions budget that is explicitly identified in the SIP will be used in the transportation conformity process to cap the emissions allowed by motor vehicles on the regional transportation network as planned.

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Sanctions. Sanctions may occur due to deficiencies involving State Implementation Plans (SIPs) and involve EPA findings of non-submittal, incompleteness, lack of implementation, or disapprovals of control strategy SIP submittals required under the CAA. Sanctions are not imposed for maintenance plan failures. Highway sanctions are used for purposes of enforcing deadlines for SIP submittals and the implementation of approved SIP measures or elements required under the CAA. Under the CAA, two types of sanctions are available to the EPA Administrator (mandatory and discretionary) for consideration upon determination of a SIP deficiency. EPA must impose sanctions through a rule making process. Once an area is officially notified by EPA of certain SIP deficiencies, the sanction's clock is triggered. Eighteen months after the sanctions clock has started, a 2 to 1 offset sanction on new or modified major stationary sources will be imposed. Under offset sanctions, each ton of emissions created by a new stationary source must be offset by a two ton reduction in existing stationary sources. Six months after offset sanctions, highway sanctions will be imposed. If the SIP failure is corrected by the State, the sanctions clock is stopped. When highway sanctions are imposed, only those specific categories of transportation actions identified as "exempt" under the CAA and those specific categories of actions shown within FHWA's exemption criteria policy may proceed forward toward final construction and implementation. Highway sanctions apply to projects where funds have not yet been obligated by FHWA by the date the highway sanctions are imposed. Projects that have already received approval to proceed and had funds obligated may proceed, if no other FHWA action is required.

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Conformity. Transportation conformity, as required by the CAA, ensures that Federally-funded or approved transportation plans, programs, and projects conform to the air quality objectives established in the SIP. Transportation conformity regulations are developed by EPA, with the U.S. Department of Transportation's (DOT's) input and concurrence. The U.S. DOT (through the FHWA and FTA) is responsible for implementing the conformity regulation in nonattainment and maintenance areas. EPA has a consultative role in the analysis and findings that are required. In terms of transportation plans and transportation improvement programs (TIPs), FHWA/Federal Transit Administration’s joint conformity determination is based on a quantitative demonstration that projected motor vehicle emissions from the planned transportation system do not exceed the motor vehicle emissions budget established in the SIP. The budget provides the upper limits for emissions in specific years that serve as milestones intended to bring the area into attainment of the air quality standards. If the transportation plan or TIP cannot meet the motor vehicle emissions budget, then changes may need to be made to the transportation plan or TIP, or the SIP. The conformity determination must also include an assurance that TCMs included in the SIP are being implemented in a timely fashion. If conformity is not determined according to the timeframes established in the regulations, a conformity "lapse" will occur. When conformity lapses, only Federal projects that are exempt from transportation conformity (e.g. safety projects), TCMs in an approved SIP, or project phases that have already received funding commitments by FHWA or FTA, may proceed.

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SAFETEA-LU Conformity Provisions. Section 6011 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act, A Legacy for Users (42 USC §7506) revised transportation conformity requirements, establishing longer update cycles as well as a one-year grace period for conformity lapses. An FHWA fact sheet provides the following description of key modifications to conformity requirements made by SAFETEA-LU:

• Requires metropolitan planning organizations (MPOs) to redetermine conformity of plan and TIP not later than two years after motor vehicle emission budgets are found adequate, the budgets are approved (if they had not yet been found adequate), or a Federal Implementation Plan (FIP) approval that establishes/revises budgets. [6011(a)]
• Requires the frequency of conformity for plans and TIPs to be every four years, except when the MPO elects to update the plan or TIP more frequently, or when SIP actions trigger a new conformity determination. [6011(b)]
• Requires that conformity determination must be made for the last year of the transportation plan, but allowing, at the election of the MPO, and after consultation with the applicable air agency and public comment, conformity to be demonstrated for the longer of: (1) the first ten-year period of the plan, (2) the latest year the SIP has a budget, or (3) the year after completion of a regionally significant project that is in the TIP or one that requires approval before the subsequent determination. Such conformity determinations would need to be accompanied by a regional emissions analysis for the last year of the transportation plan and any year shown to exceed budgets by a prior analysis. [6011(c)]
• Allows at the election of the MPO, after consultation with the applicable air agency and public comment, conformity to be demonstrated only through the end of the maintenance period once budgets are found adequate or approved for the second ten-year maintenance plan. [6011(c)]
• Provides that substitute TCMs can replace or be added to existing TCMs in approved SIPs, if (1) the substitute achieves equal or greater emissions reductions; (2) the schedule is consistent with existing TCM, or if the implementation date has passed, as soon as practicable, but no later than date reductions are needed; (3) adequate personnel, funding, and enforcement are demonstrated; and (4) the substitute is developed through a collaborative process that includes public comment and concurrence by the MPO, the air agency, and EPA. No substitution mechanism in the SIP is needed, and substitution does not require a new conformity determination or SIP revision. [6011(d)]
• Defines lapse in the Clean Air Act, and provides that a lapse will not occur until 12 months after an applicable deadline. [6011(e)]
• Provides that the Conformity SIP only needs to include consultation procedures, and enforcement and enforceability criteria and procedures to address 40 CFR 93.122(a)(4)(ii) and 40 CFR 93.125(c). [6011(f)]

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Inspection and Maintenance (I/M) Programs. Most nonattainment areas are required to implement I/M programs to ensure that emissions control devices on in-use vehicles are operating properly.  I/M programs can reduce mobile source emissions and help improve air quality by identifying vehicles with malfunctioning emission control devices, and causing them to be fixed before a new vehicle registration is issued.  Such malfunctioning vehicles, while a small portion of the overall fleet, contribute disproportionately high mobile source emissions.

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Congestion Mitigation and Air Quality Improvement (CMAQ) Program. The CMAQ program, initially developed under the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 and reauthorized under subsequent Acts, provides an important source of funds to help fund transportation projects which help reduce emissions in ozone, CO, and PM nonattainment and maintenance areas.  CMAQ funds can be used for a wide range of programs and projects such as transit improvements, HOV lanes, traffic flow improvements, demand management strategies, pedestrian and bicycle programs, I/M programs, shared ride services, etc.  While the main goal of the CMAQ program is to fund programs and projects that improve air quality, many of the projects also help to reduce congestion.

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Background. Addressing emissions of toxic air pollutants from mobile sources is an emerging area of concern for transportation agencies. Air toxics, also known as hazardous air pollutants, are substances that are known to cause or suspected of causing cancer or other serious health effects. The Clean Air Act identified 188 air toxics, and in 2002, EPA developed a list of 21 mobile source air toxics (MSATs).  EPA refined the list further, compiling a subset of six MSATs identified as having the greatest influence on health:

• benzene,
• 1,3 butadiene,
• formaldehyde,
• acrolein,
• acetaldehyde, and
• diesel particulate matter (DPM).

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U.S. 95 Settlement. The issue of air toxics was a primary concern raised by the Sierra Club in its legal challenge to U.S. 95 in Las Vegas. (Sierra Club v. Mineta, D. Nev., No. CV-S-02-0578-PMP-RJJ, settlement announced 6/27/05).

The U.S. 95 widening project, which proposed to increase the highway from six lanes to 10 lanes, was undertaken in response to estimates that by 2015, absent improvements, peak-hour traffic volume is expected to equal or exceed capacity on more than 100 miles of roadway in the Northwest Region of the Las Vegas Valley, which includes portions of the City of Las Vegas, the City of North Las Vegas, and unincorporated Clark County.

The Sierra Club had challenged the sufficiency of the environmental impact statement for the widening project, maintaining the EIS did not adequately identify and study the project's impacts, including adverse health effects from increased motor vehicle emissions.

The U.S. District Court for the District of Nevada ruled in favor of FHWA, saying the agency met its requirements in issuing the EIS. The Sierra Club appealed, and the U.S. Court of Appeals for the Ninth Circuit issued a stay on construction of the highway project pending the outcome of the appeal.

In the June 27, 2005, settlement, FHWA and the Nevada Department of Transportation agreed to install air pollution monitoring and filtration systems at three schools adjacent to the U.S. 95, relocate portable school buildings and playgrounds, help redesign a nearby high school to minimize exposures, and retrofit diesel school buses to reduce emissions.

FHWA also agreed to conduct a major study to monitor emissions at five highway locations across the country to determine the levels and behavior of toxic air pollution from motor vehicles. The results of the studies could have implications for addressing toxic air emissions from highways nationwide.

For additional information, access the Sierra Club v. Mineta settlement agreement.

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FHWA Guidance. Interim guidance to assist transportation agencies in conducting project-level MSAT analyses was issued by FHWA in February 2006.

The interim guidance suggests three options for addressing MSATs in NEPA documentation: no analysis, a qualitative analysis, or a quantitative analysis. 

Projects with no potential for meaningful MSAT effects would require no analysis for MSATs. These include projects that qualify for a categorical exclusion under NEPA, projects exempt under the CAA conformity rule, or other projects with "no meaningful impacts on traffic volumes or vehicle mix," the agency said.

Projects with low potential MSAT effects would require a qualitative analysis.  A qualitative assessment of emissions "would compare, in narrative form, the expected effect of the project on traffic volumes, vehicle mix, or routing of traffic, and the associated changes in MSATs for the project alternatives, based on VMT [vehicle miles traveled], vehicle mix, and speed," the agency said.  The analysis also would discuss "national trend data projecting substantial overall reductions in emissions due to stricter engine and fuel regulations issued by EPA," according to the guidance.

Qualitative analysis would be appropriate for projects aimed at improving operations without substantially increasing capacity or without creating a new facility that would affect emissions.  Because the emission effects of these projects are low, FHWA said, there would be no appreciable difference in overall MSAT emissions among the various project alternatives considered. 

The guidance provides model language for qualitative assessments to include in environmental documents, with specific examples for four types of projects: a minor widening project; an interchange with a new connector road; an interchange without a new connector road; and minor improvements or expansions to intermodal centers or other projects that affect truck traffic.

Projects with higher potential MSAT effects should have a more rigorous quantitative analysis. This analysis would attempt to measure the level of emissions for the six priority MSATs for each alternative, to use as a basis of comparison. This analysis also could address the potential for cumulative impacts, FHWA said. 

This category includes projects that have the potential for meaningful differences among project alternatives, and must meet a two-pronged test. The projects must:

• create or significantly alter a major intermodal freight facility that has the potential to concentrate high levels of diesel particulate matter in a single location; or
• create new or add significant capacity to urban highways such as interstates, urban arterials, or urban collector-distributor routes with specified traffic volumes.

•   Interim Guidance on Air Toxic Analysis in NEPA Documents. FHWA (Feb. 22, 2006)
  • Attachment 1 - Prototype Language for Exempt Projects
  • Attachment 2 - Examples of Prototype Language for Qualitative Project Level MSAT Discussions, for Projects with Low Potential MSAT Emissions
  • Attachment 3 - Prototype Language for Compliance with 40 CFR 1502.22
  • Attachment 4 - Mobile Source Air Toxics: Background for FHWA Interim Policy
  • Attachment 5 - MSAT Mitigation Strategies

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Additional Resources.

• FHWA’s Transportation & Toxic Air Pollutants Website
• Recent Examinations of Mobile Source Air Toxics
• Email summarizing and distributing the February 2002 and April 2003 memos and the US 95 case study report
• Project-Level Analysis of Air Toxic and PM_2.5 Emissions, February 4, 2002
• Follow-up to 2/4/02 Memorandum on Project-Level Analysis of Air Toxic and PM_2.5 Emissions, April 3, 2003
• Transportation-Related Air Toxics: Case Study Materials Related to US 95 in Nevada
• The FHWA Particulate Matter (PM) Program
• EPA's Mobile Source Air Toxics
• EPA's Urban Air Toxics Strategy

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Legislation:

• Clean Air Act: 42 U.S.C 85 7401 to 7515
• Clean Air Act Amendments of 1990
• Overview of Clean Air Act Amendments
• Clean Air Act Conformity Requirements: 42 U.S.C.7506
• Sanctions for non-compliance with Clean Air Act requirements:
  42 U.S.C.7509
• Federal Highway Administration SAFETEA-LU Web Site
• SAFETEA-LU Public Law 109-59 (or PDF, 5.3 MB)

Regulations:

• EPA Transportation Conformity site
• EPA Conformity Regulations: 40 CFR Part 51 and 93
• Sanctions for non-compliance with Clean Air Act requirements:
  40 CFR 52
• Laws and Regulations: transportation conformity

Policy & Guidance:

• Transportation Conformity Guidance for Qualitative Hot-spot Analyses in PM2.5 and PM10 areas,  PM2.5 Project-Level Conformity and Hot-Spot Analyses Frequently Asked Questions  and transmittal memorandum (March 2006)
• SAFETEA-LU Sec. 6011: FHWA Interim Guidance for Implementing the Transportation Conformity Provisions in SAFETEA-LU (February 14, 2006)
• EPA Transportation Conformity site
• New Guidance on CMAQ and Revocation of the 1-Hour Ozone Standard, December 13, 2004
• Interim Guidance on SAFETEA-LU Planning, Environment, and Air Quality Provisions - Joint FHWA/FTA Authorities; September 2, 2005
• Transportation Conformity in Complex Areas (FHWA study)
• Conformity Implementation in Multi-jurisdictional Nonattainment and Maintenance Areas for Existing and New Air Quality Standards (access link from EPA web site).
• Clarification of Transportation Conformity Requirements for FHWA/FTA Projects Requiring Environmental Impact Statements
• Nonattainment Designations under the 8-Hour Ozone and PM_2.5 Standards
• Guidance on the Implementation of the March 2, 1999 Court Decision
• Guidance for Qualitative Project Level "Hot-Spot" Analysis in PM-10 Nonattainment and Maintenance Areas - September 12, 2001 (superceded in March 2006)
• Information: Limited Maintenance Plans - September 7, 2001 
• Clarification of Plan Requirements in Nonattainment and Maintenance Areas - May 25, 2001
• Transportation Conformity Alert - April 2001
• Program Guidance on High Occupancy Vehicle Lanes - March 28, 2001
• Use of Latest Planning Assumptions in Conformity Determinations - January 18, 2001
• Transportation Conformity Alert - August 2000
• Memorandum of Understanding between DOT and EPA on Transportation Conformity - April 25, 2001
• The CMAQ Brochure
• Eligibility of Transit Station Rehabilitation for CMAQ Funding - January 30, 2003
• Eligibility of Freight Projects and Diesel Engine Retrofit Programs - January 29, 2003
• CMAQ Notice on High Speed Rail Eligibility - January 18, 2002
• Program Guidance - April 28, 1999 - CMAQ
• FHWA Program Guidance on HOV Lanes - March 28, 2001
• CMAQ Annual Report : Eighth Year (FY 1999) - Memo and report; FY 1992 - 1998 Reports
• CMAQ Weighted Populations By State, Nonattainment Area, and County
  • FY 2003
  • FY 2002
• FY 2003 CMAQ Program Apportionments by State
• CMAQ: Advancing Mobility and Air Quality (May 2003)
• Guidance: Eligibility of Truck Stop Electrification (TSE) and Other Idle-Reduction Measures - August 25, 2003
• TCSP Third Year Report 2001 Highlights

EPA Guidance:

• EPA Fine Particle (PM 2.5) Designations Website
• Official Release of EMFAC2002 Motor Vehicle Emission Factor Model for Use in the State of California
• Official Release of the MOBILE6 Motor Vehicle Emissions Factor Model
• Improving Air Quality Through Land Use Activities - January 2001 [PDF 1.80mb]
• Guidance on Applicable Methodologies to Account for the Benefits of Infill in SIPs and Conformity Determinations
• Policy Guidance on the Use of MOBILE6 for SIP Development and Transportation Conformity
• Technical Guidance on the Use of MOBILE6 for Emission Inventory Preparation
• Boundary Guidance on Air Quality Designations for the 8-Hour Ozone National Air Quality Standards (NAAQS or Standard)
• Guidance on 8-Hour Ozone Designations for Indian Tribes
  

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FHWA Resources.

• Air Quality Planning for Transportation Officials
• Congestion Mitigation and Air Quality Improvement Program (CMAQ)
• General Air Quality Publications
• Global Climate Change
• Highway Sanctions
• Microscale and Regional Modeling and Emissions Models
• Outreach and Education - It All Adds Up to Cleaner Air
• Particulate Matter and Air Toxics
• Transportation Control Measures
• Trends Analysis
• Vehicle Miles Traveled (VMT) and Vehicle Emissions
• Transportation Conformity
• Links to Transportation Control Measure sites
• FHWA Air Quality Performance Measures

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EPA Resources. EPA’s Office of Transportation and Air Quality (OTAQ) provides information on a range of transportation/air quality issues including:

• Pollutants and Programs: Information on how much air pollution and greenhouse gases are emitted by mobile sources, the programs OTAQ has undertaken to control these emissions, and the impact of those programs on air quality and climate change.
• Consumer Information: Ways to help reduce air pollution and buy the cleanest, most fuel-efficient vehicle.
• On-road Vehicles and Engines: Information about highway vehicles (cars and light trucks, heavy trucks, buses, and engines, and motorcycles): fuel economy, emission standards and regulations, emission recall programs, new vehicle certification and in-use vehicle compliance, inspection and maintenance programs, diesel retrofit programs, evaluating the benefits of inventions designed to reduce emissions, and importing vehicles to the United States.
• Nonroad Engines, Equipment, and Vehicles: Information about aircraft, locomotives, diesel and gasoline boats and ships, personal water craft, lawn and garden equipment, agricultural and construction equipment, and recreational vehicles (e.g., dirt bikes, snowmobiles): emission standards and regulations, certification and compliance, and diesel retrofit programs.
• Fuels and Fuel Additives: Information on diesel, gasoline, and alternative fuels for mobile sources, fuel quality control programs, the requirements for registration and health effects testing of new fuels or fuel additives, and reporting forms.
• Voluntary Programs: Information about voluntary programs to reduce air pollution associated with transportation and other mobile sources, including commuter choice programs, diesel retrofit, choosing a cleaner car or truck, and other initiatives.
• Transportation and Air Quality Planning: Information on the ties between land use and transportation planning, and air quality. Topics includes conformity, State Implementation Plans (SIPs), transportation control measures, and available funding and grants for implementation of such programs.
• Modeling, Testing, and Research: Information on OTAQ models for estimating emissions from on-road vehicles, nonroad sources, and fuels; information on how EPA tests and measures emissions; and information on OTAQ research into advanced technologies.

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• FHWA Transportation Conformity Community of Practice
• EPA's MOBILE6 Vehicle Emission Modeling Software
• EPA's Adequacy Review of SIP Submissions for Conformity
• Research Products
• Contacts
  

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