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Last Updated: Wednesday, March 14, 2012 1:59 PM

Chapter 11 - Air Quality


This topic covers the regulatory framework and recommended procedures for performing an air quality analysis for both Caltrans and local agency transportation projects. Preparation of the air quality section of the environmental document and supporting technical report are discussed in detail. There is also discussion of air quality requirements throughout the project delivery process, from transportation conformity determinations at the regional planning stage to project requirements during construction.


- See also Chapter 1 - Federal Requirements and Chapter 2 - State Requirements for laws and regulations that apply to all environmental analysis activities. See Chapter 38 - NEPA Delegation for additional requirements.

The primary laws related to air quality issues are the Federal and California Clean Air Acts, Federal Planning regulations and enabling legislation, US EPA conformity regulations, and local and air district ordinances and regulations related to specific activities.

Effective July 1, 2007 FHWA has assigned, and the Department has assumed, all the United States Department of Transportation (USDOT) Secretary's responsibilities under NEPA, also known as NEPA Delegation (6004 MOU and 6005).  The assignment applies to all projects on the State Highway System (SHS) and all Local Assistance Projects off the SHS within the State of California, with the exception of the responsibilities concerning certain categorical exclusions.

For both programs, the Department has also assumed the USDOT Secretary’s responsibilities for environmental review, interagency consultation, and other regulatory compliance-related action pertaining to the review or approval of projects for which the Department assumed responsibilities under NEPA pursuant to the federal environmental laws listed in Section 3.2 of the Pilot Program MOU (see also Appendix B of the Section 6004 MOU).  The Department is responsible for complying with the requirements of all applicable environmental law regardless of its inclusion on the list of applicable laws [MOU 3.2.2]

As such, FHWA’s air quality conformity responsibilities may not be assigned to the Department under the Pilot Program [MOU 3.2.4].   Air quality conformity determinations for CEs assigned to the Department under the Section 6004 MOU have been assigned to the Department [Section 6004 MOU, Appendix B].

Note: Most links are to other agencies' web sites.

Federal Air Quality Laws and Regulations

State Air Quality Laws and Regulations

Key Web Sites

Air Quality Guidance and Information

Contact Lists and Related Information


Regulatory Framework

Nearly all transportation projects have some effect on air quality. On-road motor vehicles are, in many areas, the major source of air pollutant emissions contributing to violations of air quality standards. Projects that affect the capacity or location of major roads or other elements of the transportation system can cause adverse air quality impacts. However, in many cases, the impact may be positive–a capacity or alignment change often improves traffic flow enough, at least for a period of time, to reduce pollutant emissions. In the long term, emissions from the entire fleet of motor vehicles will drop due to improved vehicle emission controls, but future traffic growth will, to some degree, counteract these reductions. For some pollutants, vehicle-related emission controls may not have a major effect; for example, re-entrained road dust emissions are roughly proportional to vehicle miles traveled. Also, short-term emissions from construction processes and equipment may be an issue if not adequately accounted for in existing regional air quality plans and regulations.

Most of California transportation air quality requirements come from two statutes, the federal Clean Air Act (FCAA) and the California Clean Air Act (CCAA). The FCAA, as amended in 1990, sets nationwide standards, called National Ambient Air Quality Standards (NAAQS). The U.S. EPA administers the FCAA, sets the specific air quality and emissions standards and delegates certain responsibilities to other federal agencies and to the states. EPA has set both primary (health) and secondary (welfare) standards for the six "criteria pollutants"– carbon monoxide, lead, nitrogen dioxide, ozone, sulfur dioxide, and particulates (PM10 and PM2.5).

In addition to the criteria air pollutants for which there are National Ambient Air Quality Standards (NAAQS), EPA and ARB also regulates Toxic Air Toxic Contaminants (TACs, or air toxics).  Most air toxics originate from human-made sources, including on-road mobile sources, non-road mobile sources (e.g.) airplanes), areas sources (e.g. dry cleaners) and stationary sources (e.g.) factories or refineries). Mobile Source Air Toxics (MSAT) are a subset of the 188 air toxics defined by the Clean Air Act.  The MSATs are compounds emitted from highway vehicles and non-road equipment.  FHWA released their Interim Guidance on Air Toxic Analysis for NEPA documents on September 30, 2009. It can be viewed on the FHWA Web site at: FHWA Interim Guidance.

While the FHWA Interim Guidance provides for the national level, California's vehicle emission control and fuel standards are more stringent than Federal standards. As such the State's standards are effective sooner, so the effect on air toxics of combined state and federal regulations is expected to result in greater emission reductions, more quickly, than the FHWA analysis shows. The FHWA analysis, with modification related to use of the California-specific EMFAC model rather than the MOBILE model, would be conservative.

The California Clean Air Act sets up a structure managed by the Air Resources Board (ARB) similar to the Federal one for air toxics.  All Federal air toxics are incorporated into the California lists by reference.  In addition, California regulates a large number other substances not currently on the Federal list.  Key California-only air toxics for consideration in transportation projects include diesel exhaust particulate matter and naturally-occurring asbestos. 

The ARB’s air toxics program web page is at: Exit CT. Note that not all of the ARB toxics programs apply to transportation projects; consult with technical or Legal staff before getting into a lot of detail.

Under the FCAA, EPA has designated planning areas throughout the country. Areas are classified as being in "attainment" for a given pollutant if they meet the prescribed standards. If an area does not meet the standard, it is designated as a "nonattainment" area for that pollutant. Areas that were previously designated as non-attainment areas but have now met the standard–with EPA approval of a suitable air quality plan–are called "maintenance" areas.

The Federal Clean Air Act requires that states produce improvements in air quality over time. This means reducing air pollution to healthful levels in nonattainment areas and developing controls to ensure the air remains healthful in subsequent years. The State Implementation Plan (SIP) process is the means by which states develop a collection of regulations and plans to demonstrate this effort to the federal government. In order to meet their transportation planning goals, Metropolitan Planning Organizations (MPO) and Regional Transportation Agencies (RTPA) create long-range plans and programs, such as Regional Transportation Plans (RTP) and Regional Transportation Improvement Programs (TIP), which include proposed transportation projects. The projects included in these plans and programs must be consistent with (or conform to) the approved SIP, and hence the requirements of the FCAA. This process is called Transportation Conformity. If a project would contribute to the violation of a standard, it cannot be included in the conforming plan and cannot be built. For more about how air quality is addressed at the planning stage, see Vol. 1 Chapter 4: Environmental Considerations During Transportation Planning.

In nonattainment or maintenance areas, transportation conformity applies if projects will be funded by the Federal Highways Administration, Federal Transit Administration, or any agency that has been delegated project approval by these agencies. It also applies if projects are determined to be regionally significant as defined at 40 CFR 93.101 and are approved by a regular recipient of federal highway or transit funds, such as Caltrans and most local transportation agencies.

A further demonstration of transportation conformity–at the project level–is required if a project is located in a nonattainment or maintenance area. The basic demonstration of conformity consists of showing that the project is listed in and consistent with a conforming RTP and TIP. In addition, a microscale or "hot-spot" analysis for conformity is required if a project is located in a nonattainment area for CO, and/or PM2.5 and PM10. Emission reduction measures may be required to ensure that the project will not cause or contribute to new violations of a standard. Caltrans cannot approve a project that would cause or contribute to violation of a federal air quality standard. FHWA and EPA released a national guidance memo on March 29, 2006 for doing qualitative PM2.5 and PM10 hot spot analysis. See attachment at the bottom of this memo.

The California Clean Air Act (CCAA) must be addressed in CEQA documents for transportation projects. Although state air standards for some pollutants are more stringent than federal standards, there is no conformity process under the state law.  Over time, as air quality improves under the federal conformity process, it is expected that there will be progress in meeting state standards as well. The California Air Resources Board (ARB) is responsible for establishing state air quality standards and enacting regulations for statewide air pollution control programs, and for submitting the SIP to the U.S. EPA.  Local air pollution control districts and air quality management districts directly regulate stationary and some area sources of emissions, but not mobile sources, under the structure set up by the CCAA. The air districts perform most of the air quality planning in California, including the development of SIP submittals under the FCAA.

Various Pollutants

Caltrans and Caltrans-approved local agency projects must analyze a variety of air pollutants in order to assess our project's potential to impact the environment. The following is a brief breakdown of the most common pollutants.

  • Ozone impacts are regional in nature and cannot be ascribed to any single project. Ozone is formed by reactions, in the presence of sunlight and heat, primarily between organic compounds and nitrogen oxides. These precursor compounds are emitted by all combustion sources, and in many regions mobile sources including motor vehicles are the major source. Ozone violations most often occur in summer (April-October), since strong sunlight and heat are necessary for its formation. Projects that are included in the RTP and TIP have been included in a regional conformity analysis and require no further analysis for ozone at the PID or subsequent project phases.
  • Particulate Matter (PM10 and PM2.5) refers to airborne particles that are less than 10 microns in diameter (PM10) and less than 2.5 microns in diameter (PM2.5). Particulate matter is both a regional and project-level issue. Particulate matter is both directly emitted and, especially for PM2.5, a result of secondary formation based on nitrogen oxides (NOx), volatile organic compounds (VOC), sulfates (SOx), and ammonia (NH3). As with ozone, secondary pollution forms some distance away from the precursor emission sources, and up to several hours later. Regional PM is primarily a winter nighttime product, since cool, damp, stable weather is needed to support the chemical reactions that produce it. Directly-emitted PM2.5 and PM10 has been determined to be a conformity issue in California. FHWA has approved a qualitative analysis approach for use at the project level. 
  • Carbon Monoxide is emitted directly from vehicles and is a major issue at the project level. Transportation projects in nonattainment or maintenance areas for CO are testing using approved emissions models such as the Caltrans/UCD CO Protocol and the CALINE4 model.
  • Asbestos is an air quality, as well as a hazardous materials, issue. If structural demolition is needed, such as removal of an existing bridge, the release of friable asbestos may be an abatement issue. In areas where naturally occurring asbestos is an issue, geologic studies, mandatory air district notices, special construction provisions, and other activities may be needed. Structural asbestos (demolition) is regulated by Federal and related State/air district regulations (NESHAP Link exits Caltrans web site - privacy and other policies may differ). Naturally occurring asbestos is regulated under ARB regulations Link exits Caltrans web site - privacy and other policies may differ and worker-safety programs.
  • Construction stage impacts from dust are an issue in some areas of the state. This is especially true if sensitive land uses (such as schools, health–and child-care facilities) are nearby. Dust emissions are an important consideration, but are largely mitigated by standard dust control techniques. In a growing number of areas, more stringent regulations requiring specific work practices and plans for dust control are required; these regulations apply to work using Caltrans specifications and special provisions based on Section 7-1.01F of the Standard Specifications ( large, pdf file). Federal conformity regulations require analysis of construction impacts for projects when construction activities will last for more than five years.
  • Diesel Exhaust Particulate Matter is a growing area of interest, although no single analysis method, or criterion for determining when detailed analysis is needed, has yet been defined by the air quality regulatory community. Quantitative health risk analysis is generally not done for transportation projects, but there is a growing emphasis on identifying and avoiding impacts to sensitive receptors, such as schools.
  • The Clean Air Act identifies 188 air toxics, also known as hazardous air pollutants. The federal EPA has identified 21 of these toxics as Mobile Source Air Toxics (MSATs). They have also identified a subset of MSATs that are known as Priority MSATs. These are: benzene, formaldehyde, acetaldehyde, diesel particulate matter/diesel exhaust organic gases, acrolein, and 1,3-butadiene. FHWA released their Interim Guidance on Air Toxic Analysis for NEPA documents on September 30, 2009. See Note.


Early Coordination Meeting

Air quality is one of the more complex of the resource areas treated in environmental documents. For many projects there is a substantial amount of interagency work done at the transportation planning stage. When a project moves into the PID stage, environmental planners and air quality specialists should attend any early coordination meetings held for air quality.

For major projects, the local air district should be involved in at least one early meeting during project initiation. Also, the local air district should be invited to any public or agency scoping meeting held at the environmental phase.

Here are some good questions to consider at this stage:

  • Is the project in an area where Federal Clean Air Act conformity requirements apply? If so, does the project come from a conforming Regional Transportation Plan? 
  • Are any other project-level conformity issues present? Will a hot-spot analysis be needed for conformity?
  • Is adequate traffic information available to determine the LOS, vehicle fleet mix, and traffic volumes both on the project (for Baseline, No Project, and viable Build Alternatives) and for nearby major intersections?
  • If an air quality analysis has already been prepared, does it adequately document project effects on localized emissions of CO and/or PM 2.5 and PM10?
  • Could asbestos–structural demolition or naturally–occurring–be an issue?
  • What standard minimization and avoidance measures, such as dust control during construction, could be part of the project?
  • Are there schools, health facilities, or other sensitive receptors in the project area?

Interagency Consultation for Conformity

Conformity requirements apply in areas that are designated nonattainment or maintenance for federal air quality standards. For projects that affect highway capacity, or other projects where questions arise regarding conformity issues, a regional interagency consultation process is available to discuss and gain consensus on conformity issues. Areas in California that are subject to conformity requirements are shown at the Caltrans air quality web page. A map and a table of affected areas (with links to relevant transportation planning and air quality agencies) are available.

Interagency Consultation requirements are defined in the U.S. EPA Conformity Rule at 40 CFR 93.105 Link exits Caltrans web site - privacy and other policies may differ. Most metropolitan areas have adopted consultation procedures involving local, state, and federal transportation planning, transit, and air quality agencies. Interagency Consultation for Conformity and air quality planning is managed by the MPO in most areas.

Because FHWA retains air quality conformity determinations under Section 6005, FHWA has developed Transportation Conformity and NEPA Assumption Questions and Answers. FHWA has also developed a checklist for Conformity Analysis Documentation.


There may be several distinct air quality analyses or studies performed in support of the project development process, both at the PID and environmental document phases. For many projects, a technical report is completed to summarize studies, outline conformity information, and provide other needed information for the environmental document.

Determining the Need for a Technical Report

This should be determined at the scoping stage of the project and documented in the PID.

The project will probably NOT need a technical report if:

  • it is exempt from all conformity analysis requirements (see the "Table 2" exemption list in 40 CFR 93.126 Link exits Caltrans web site - privacy and other policies may differ; AND
  • it has no potential air quality impacts subject to NEPA analysis according to the initial screening procedure of the CO Protocol, and qualifies for a Categorical Exclusion under NEPA, AND
  • it qualifies for a Categorical Exemption under CEQA.

For projects in areas subject to Conformity, conformity documentation should be prepared and filed with the NEPA CE even if no other air quality analysis is determined to be necessary. The documentation should also cover consultation with FHWA/FTA, the MPO, and air agencies, where needed.

For most other projects, an air quality technical report should be prepared, although the report can be fairly short for projects where air quality issues are minimal and can be avoided or minimized with standard measures. Here are some examples where a comprehensive report is recommended:

  • The environmental document will be a higher level document with many complex issues, including air quality.
  • Early scoping, air analyses, or the PID indicate that air quality mitigation beyond standard impact minimization and avoidance measures may be needed.
  • The project is regionally significant for conformity analysis purposes, regardless of the type of environmental documentation to be prepared. All capacity-increasing State Highway projects, including auxiliary lanes, passing lanes, and many truck climbing lanes, are considered regionally significant by definition under federal conformity regulations.

Report Content

An air quality study report should include:

  • A basic project description documenting project design assumptions–such as future traffic–that are relevant to the air quality analysis. The project description should include a brief description of the alternatives under consideration. Make sure it is consistent with the environmental document.
  • Regional meteorology and climate discussion. Include a description of the area's topography as well, if pertinent to the discussion.
  • Regulatory Framework. Provide a description of the applicable regulations as well as the agencies, such as air districts and MPOs that are involved with air quality in the area or region.  Also outline regulations on the federal, state, local levels. Include a table outlining air quality standards on both the federal and state levels.
  • Project area and affected environment: Include monitor locations and data, area conformity designations and classifications, location of sensitive receptors.
  • Results of air quality analyses. Include a description of methodologies and assumptions used.
  • Potential impacts of the project on air quality: direct, indirect, temporary, and permanent.
  • Potential avoidance, minimization and/or mitigation measures.
  • Project-level conformity documentation, if the project is in an area subject to conformity requirements under the Federal Clean Air Act.
  • An appendix with the results of any emissions modeling done for the analysis.

Preparer Qualifications

Air quality reports should be prepared by an air quality specialist.

If asbestos is an issue, that portion of the report should be coordinated with a hazardous materials specialist. Certain asbestos studies must be done, by law or regulation, by or under the direction of a Registered Geologist, a Certified Industrial Hygenist (CIH) or a Certified Asbestos Consultant (CAC).

Processing and Approval

The report should be reviewed, at a minimum, by the Caltrans District Project Manager, Project Engineer, air quality technical specialist, hazardous waste technical specialist and environmental planner responsible for the environmental document. Procedures for final approval for air quality reports at the environmental document stage are determined by the individual Districts. Approval should be completed before circulation of the draft environmental document.

Recommended Methodologies

The methods for analyzing air quality impacts can be quite complex. This section is meant to guide the environmental planner in scoping and/or reviewing the technical report, and then writing the environmental document. The analyses are typically done by an air quality specialist in environmental engineering. Note that avoidance, minimization, and mitigation measures are discussed in the environmental document section of this chapter.


The following are permanent impacts directly and locally attributable to implementation and operation of the project. The analyses for CO, PM2.5 and PM10 are used, in addition, to document project-level conformity, where required.

  • CO (carbon monoxide) hot spot analysis: the air quality analyst should use the CO Protocol. All projects affecting traffic flow should be evaluated for potential CO impacts. Modeling may be needed. If there are questions on CO models, see the Caltrans Headquarters Air Quality Page.
  • PM2.5 (particulate matter/dust) analysis for conformity: This is a qualitative analysis. If there are questions, consult the FHWA PM2.5/PM10 Qualitative Analysis Guidance (March 2006). or at EPA site .
  • PM10 (particulate matter/dust) analysis for conformity: This a qualitative analysis. If there are questions, consult the attachment at the bottom of the memo at FHWA PM2.5/PM10 Qualitative Analysis Guidance (March 2006). . Some form of PM10 direct impact analysis must be done for all projects involving substantial facility relocation or capacity changes. Quantitative analysis methods have not been standardized, and should NOT be used at this time.
  • Mobile Source Air Toxics (MSAT): For Guidance on how to address mobile source air toxics in an environmental document, please refer to the FHWA Interim Guidance on Addressing MSAT (September 30, 2009).
  • Diesel exhaust: This a particular issue on facilities with large volumes of truck traffic. It is known that exposure to diesel exhaust over time can have effects on health. Criteria and quantitative methods for assessing diesel impacts are not yet developed at the regulatory level. However it is important to document any sensitive land uses in the vicinity of the project.
    • Sensitive Land Uses are schools, medical centers and similar health care facilities, child care facilities, parks and playgrounds.
    • Vicinity of the project is 500 feet or 150 meters from the edge of the nearest traveled lane.

Mobile Source Air Toxics (MSAT) in the NEPA Process for Highways

These are temporary impacts related to construction activities.

  • Dust Control. See Standard specifications 10 and 18. Local and air district regulations may also apply. Standard Specification 7-1.01F may also apply.
  • Structural Asbestos: Document the need for (or results of) asbestos inspection for structures that will be demolished or substantially renovated.  
  • Naturally Occurring Asbestos: Document the need for (or results of) site surveys regarding naturally occurring asbestos. This impact is largely construction-related, but may occur through ongoing maintenance activities as well.


 See the environmental document section for a discussion on this issue.


Conformity is both a project-level and a regional planning issue. Extensive modeling is required at the planning stage to do a regional conformity analysis for RTPs and TIPs, both of which must describe the specific projects that are included. See the overview section for more on this topic.

Section 6005

Air quality conformity determinations are excluded from the Pilot Program by statute [(see 23 USC 327(a)(2)(b)]. Conformity determinations, both regional conformity and project-level conformity, will remain the responsibility of FHWA California Division for all projects assumed under the Pilot Program.  For EAs and EISs under the Pilot Program, FHWA will make the conformity determinations after the preferred alternative is identified and prior to completion of the final environmental document.  For CEs under the Section 6005 Pilot Program, FHWA will make the conformity determinations prior to the approval of the CE classification. Both the regional and project-level conformity determinations must be documented in the air quality section of the final environmental document.  A copy of the FHWA conformity determination letter must also be included in the final EA or EISThe Department may not issue a FONSI or ROD without the conformity determination(s) from FHWA.

For conformity determinations where the project has been assumed under the Pilot Program, the Department will send FHWA, separate from the environmental review process, a request for conformity determinations.  In this regard, FHWA will be treated much like other federal resource agencies.   FHWA’s preference is that the air quality conformity documentation submitted to FHWA be a stand-alone report.  The air quality conformity documentation must include adequate summary information such that conformity determinations can be made on the preferred alternative without having to refer to the environmental document.  For additional information regarding documentation, please refer to the updated conformity determination checklist in FHWA’s Air Quality Conformity Questions & Answers, Attachment 2 (Conformity Analysis Documentation Checklist).  The conformity documentation should not include air quality issues that are not required for transportation conformity purposes (e.g., air toxics, asbestos, etc.).

Section 6004

For projects that are eligible for assumption under the Section 6004 MOU, both regional and project-level air quality conformity determinations for individual projects have been assigned to the Department and those determinations are made by the district/region. For additional information, see Chapter 38: NEPA Delegation for additional information.

Project Level Conformity

At the project level, existence of a valid regional conformity analysis must be documented, and in some cases more specific "hotspot" analysis and other findings may be needed. Here are some good resources on transportation conformity (all ):

Components of a Project-Level Conformity Analysis

The project level conformity documentation is done by the air quality analyst and documented in the technical report. The environmental document preparer will summarize the results in the environmental document. Ensuring conformity and documenting it are a stepwise process Here are the basic steps:

  • Determine if the project area is subject to conformity requirements (within a nonattainment or maintenance area for a federal criteria air pollutant).
  • If so, determine if the project exempt from conformity, or at least from regional conformity analysis, requirements
  • If not exempt, confirm:
    • Status of Regional Transportation Plan (RTP) and Transportation Improvement Program (TIP) conformity, or if an Isolated Rural area the date and status of the most recent regional conformity analysis.
    • Is the project listed in the conforming RTP and TIP, or in a previous regional emission analysis if in an Isolated Rural area.
      • If not, what are the results of a regional emission analysis done for the project (usually only in Isolated Rural areas).
    • If in a carbon monoxide (CO) and/or particulate matter (PM2.5, PM10) area, results of "hot spot" analysis with respect to conformity requirements.
    • Whether the project implements a Transportation Control Measure (TCM) identified in the applicable air quality plan (SIP) and RTP; if not a TCM, does the project interfere with implementation of any TCMs

More details on some of the key concerns in this documentation outline are provided below. See the air quality analyst if there are questions on conformity.


Conformity Exemption

Certain types of projects are exempt from conformity requirements. These project types are found by US EPA to be neutral from an air quality or emissions standpoint, and are listed in the Conformity Regulations at 40 CFR 93.126, 40 CFR 92.127, and 40 CFR 92.128 (all ). If a project fits one of the listed types, it may need little or no conformity analysis, and does not need to be individually listed and considered in regional conformity modeling.

Regional Conformity

If a project is not exempt from conformity requirements, and is regionally significant (see definition at 40 CFR 93.101), it must come from a conforming RTP and TIP. Documentation of the nonattainment or maintenance status of the area, including SIP submittal/approval dates, is needed. Also, documentation of the RTP and TIP conformity status (most recent amendment dates, date of last full and updated conformity determinations) is needed. The Design Concept and Scope of the project must match the Design Concept and Scope used in the RTP and FTIP project listing. "Design Concept" means the type of facility that is proposed, such as a freeway as opposed to an expressway or arterial highway. "Design scope" refers to those aspects of the project that would clearly affect capacity and thus any regional emissions analysis, such as the number of lanes and the length of the project. For Draft EIS or EA documents, at least one viable alternative must match the RTP and TIP project listing; for the Final NEPA document, the selected alternative must match the RTP and TIP project listing.

Hot Spot Analysis

If a project is located in a CO and/ or PM 2.5 and PM10 non-attainment or maintenance area, a hot-spot analysis is required for conformity purposes. Ordinarily, the hot spot analysis done for the environmental document will be adequate to allow for conformity hot spot findings. See the Caltrans HQ Air Quality Website for details on current acceptable methodologies. CO hot spot analysis tools and guidance can be found at Also refer to the attachment at the bottom of the FHWA PM2.5/PM10 Qualitative Analysis Guidance (March 2006).

In any area (attainment or nonattainment), a project must not cause exceedance of the Federal NAAQS for CO, PM10, or PM2.5. In CO, PM2.5, and PM10 non-attainment areas, not only must the project not cause a new exceedance of the NAAQS, but it must also not contribute to increasing an existing exceedance (make it worse), and if an exceedance exists in the project vicinity (generally about 1/4 mile) the project must in some way reduce it. If one or more of these tests fails, the project cannot proceed. In such a situation the project must be modified to produce changes in traffic operation that allow the hot spot tests to be met, which in some cases may require additional work at intersections in the vicinity that otherwise might not be part of the project.

Areas where the conformity hot spot tests are needed can be found in the list of areas subject to conformity at the Caltrans web site. The conformity hot spot test is required only if the project area is non-attainment or maintenance for the FEDERAL CO and/or particulate matter standards. The general procedures for carrying out hot spot analysis, however, are the same whether or not the area is subject to conformity requirements for CO or particulate matter.

In attainment (but not attainment-maintenance) areas, with prior approval by FHWA, and/or HQ, the 2005 FHWA/CT/UCD procedure may be used.

SIP Control Measures

All projects in areas subject to conformity must demonstrate that they do not interfere with implementation of Transportation Control Measures (TCMs) listed in the State Implementation Plan for the area. (TCM's are regional measures used to reduce emissions. They are a broad array of strategies and can range from specific traffic control measures to the incorporation of carpool programs. If a project comes from a conforming RTP and TIP the RTP and FTIP conformity analyses would have documented system-level timely implementation and non-interference with TCMs.

Suggested Language for Conformity Documentation

CE Documentation: - Attach a sheet to the standard CE/CE form with conformity documentation. Backup materials such as a localized (CO, PM 2.5, PM10) impact analysis or screening, as needed, should be included in the project file. Projects that are processed with CEs under CEQA and NEPA will usually, but not always, be exempt from regional conformity requirements as well.

EA or EIS: - Use the flowchart included in the standard environmental document outlines in the SER. Where additional documentation is needed, consult with the air quality analyst for content for the environmental document.

Conformity Flow Chart

Conformity Flow Chart



Caltrans now uses a standard format for impact discussions in its environmental documents. See the SER forms page for the following format outlines:

  • IS/EA outline with annotated guidance, including an air quality section
  • EIR/EA outline with annotated guidance, including an air quality section
  • EIR/EIS outline with annotated guidance, including an air quality section
  • EIS outline with annotated guidance, including an air quality section
  • EA outline with annotated guidance, including an air quality section

The outlines, including use of standard language for the regulatory setting, are mandatory for all Caltrans documents and strongly recommended for local agency projects that will be approved by Caltrans. This section is meant to compliment and, where needed, expand on the information and guidance provided in the outlines.

The air quality section of the environmental document should discuss the following items, as appropriate:

  • Regulatory Setting
  • Affected Environment
  • Impacts (including permanent, temporary, direct and indirect)
  • Avoidance, Minimization and/or Mitigation Measures
  • Cumulative Impacts

Construction Impacts can be included or treated as a separate section in the environmental document.

Summarize the information in the technical report, as needed, to draft the environmental document. Remember to write the document for the general reader. Technical detail should be kept to a minimum. If needed, refer the reader to the technical report.

Regulatory Setting

Use the standard (boilerplate) language in the approved outline if applicable. If not using the outline, include a brief discussion of the regulatory framework for the analysis, including local, state, and federal laws. Provide a summary of regional transportation planning.

Affected environment

  • Briefly describe climate and meteorology,  focusing on what will most affect air quality.
  • Describe current air quality status of the area for both state and federal criteria pollutants.  Include a chart of air quality standards for reference. Here is a chart that may be useful: ARB air quality standards chart Link exits Caltrans Web Site - privacy and other policies may differ Link requires Acrobat Reader to view - click icon to go to Adobe web site and download reader if needed
  • List air quality monitoring stations and recent data (generally the immediately past 3 years) in the project area, and any other localized air quality-related information pertinent to the air quality analysis.
  • Document if naturally-occurring asbestos is found in the project area.


Note: Be sure to address impacts of the no build and ALL alternatives in the environmental document.

Direct Impacts

The following are permanent impacts, directly and locally attributable to implementation and operation of the project.

  • Summarize results of microscale/hot spot analyses for carbon monoxide (CO).
  • Summarize results of microscale/hotspot analysis for particulate matter (PM 2.5 and PM10).
  • Although there is no currently methodology for directly assessing diesel impacts, document any sensitive uses in the area, as described in the technical report section.

The following are temporary, construction related impacts.

  • Summarize naturally-occurring or structural asbestos review. Cross-reference with hazardous materials chapter as appropriate.
  • Provide results of studies aimed at any location-specific issues that may occur.  In San Joaquin Valley, South Coast, and Coachella Valley areas (as of 3/2005), summarize how project design and operational/construction practices will comply with PM2.5 and PM10 regulations.
  • Construction impact analysis should document the PM 2.5 and PM10 (dust) impacts expected.
  • If construction will last more than 3 years, or will substantially affect traffic due to detours, closures, and temporary terminations, then the CO and PM10 hot spot impacts of the disturbed traffic flow should be analyzed. In areas subject to Transportation Conformity requirements, construction that will last more than 5 years makes a construction impact analysis necessary.

Indirect and Cumulative Impacts

Air pollutant emissions from a project may have an indirect or cumulative effect at a regional scale, since they combine with all other emissions in a region to produce certain pollutant concentrations.   If a project is included in from a regional plan and transportation improvement program that contributes to attainment or maintenance of applicable air quality standards–as documented in a program level environmental document or a conformity analysis–it would not typically have a cumulative adverse impact on regional air quality.

There may be cases where a separate methodology is needed for assessing indirect and/or cumulative impacts.

See the SER for guidance on cumulative impact analysis. Guidance on indirect impacts is also available in the SER. 

Avoidance, Minimization, and/or Mitigation Measures

For direct, operational impacts, summarize any avoidance, minimization and/or mitigation measures. Include, for example, project design features such as paved shoulders, which will reduce PM2.5 and PM10 emissions from re-entrained road dust. Include also any design changes that were included to avoid CO exceedances. Include design changes made to avoid or minimize exposure of sensitive receptors.

For construction related, temporary impacts:

  • Summarize avoidance, minimization and/or mitigation measures for issues such as naturally-occurring or structural asbestos.
  • Describe any standard or special provisions that will be included in the project to minimize dust exposure during construction.


  • Note that compliance with any applicable local, air district, state, and Federal air quality laws and regulations applicable to construction activity is required by Standard Specifications Section 7-1.01F.
  • List/summarize any air quality permits or notifications expected to be needed for construction.


In areas where conformity applies, include a brief discussion and documentation of project-level conformity. Refer the conformity discussion in the Reporting Section for details.


Project Initiation Document

Analysis and or studies at the PID stage consist of verifying consistency with regional air quality plans and programs, and scoping project-level studies.  If a Preliminary Environmental Analysis Report (PEAR) for Caltrans projects or a PES for Local Agency projects is prepared, air quality should always be evaluated and reported on in the report.

For projects in areas subject to conformity requirements, a conformity review should be done as part of the PEAR or environmental document. The review should document whether conformity applies, whether the project is exempt from conformity, whether the project is listed in the conforming RTP if not exempt, whether regional significance questions are relevant, and scoping information for a full conformity analysis as part of the environmental process.

For rehabilitation and maintenance-type projects, air quality analysis may be completed at this stage if no formal environmental document will be prepared.

Draft Environmental Document

This is the stage where the bulk of air quality analysis is done. Detailed analyses for all viable alternatives, and No Project, are completed.  If field air quality monitoring is done (exceptional cases only), it would be completed a this stage, but might need to start during the Project Initiation Document due to timing requirements (CO monitoring must be done for the entire period between October and April; PM monitoring if done must occur for several months during the period when known exceedances of the PM standards occur).

Preliminary project-level conformity, impacts, and proposed mitigation measures are all determined at this stage.  At least one viable alternative must match the project listing in regional transportation planning and conformity documents.

Final Environmental Document

If comments are made regarding air quality during circulation of the draft environmental document, they must be addressed at this stage and modifications must be made to the air quality studies as appropriate.  If project alternatives change due to comments, air quality effects may need to be re-examined.

The final project-level Conformity determination and determination of environmental impacts and required mitigation measures are made at this stage.  Mitigation commitments are finalized.  The final, selected alternative must match the project listing in regional transportation planning and conformity documents; if it doesn't, the regional transportation plan, transportation improvement program, and/or conformity determination must be modified before the final environmental document can be completed.

Project Design/Construction

Air issues should be re-examined and updated as necessary whenever an Environmental Reevaluation is done.

If regional Conformity lapses during Design, work on the project may not be able to proceed to the next phase. A regional Conformity "Freeze" can prevent changes that affect the design concept and scope of the project. In areas where conformity requirements are newly applied after the environmental process is complete, it may be necessary to perform the first conformity analysis, and obtain a conformity determination from FHWA and FTA, at the time PS&E is submitted.

In order to retain the conformity determination made for the Final Environmental Document, no more than 3 years may elapse between each of the following milestones:  Final NEPA approval; start of Design work; acquisition of "a substantial portion" of the needed right of way; and completion of PS&E.


Regional Transportation Plan

This information should be documented in the environmental document prepared by the MPO or RTPA for the Regional Transportation Plan (RTP) and serve as a building block in subsequent decision making.

  • The RTP should establish a purpose and need for regionally significant projects.
  • The RTP should include a listing of all regionally significant projects assumed to be constructed and open to travel in each of the analysis periods used for the air quality analysis.  Individual project listings should include a brief description of the design concept and scope of the project.

Project Initiation Document

The following information should be included in the Preliminary Environmental Analysis Report (PEAR) prepared as part of the Project Initiation Document (PID).

  • Verify air quality information from RTP stage.  If the project was specifically listed in the RTP conformity analysis, verify design concept and scope information and make sure any new alternatives are included.  If design concept and scope have changed substantially from that used in the RTP Conformity analysis, a RTP amendment may be needed to complete the programming process.
  • Determine whether conformity applies, and if so whether a conformity exemption applies.  
  • Plan any needed Early Coordination meetings.
  • Plan the cost, scope, and schedule for any air studies to be completed at the environmental document stage.
  • If needed, perform localized impact (hot-spot) analysis.

Draft Project Report

This information should be included in the Draft Environmental Document (DED) or used as supporting documentation for a CE, as appropriate.

  • Make sure the design concept and scope (40 CFR 93.101) of at least one alternative matches the conforming RTP and TIP project descriptions.
  • Make sure the purpose and need and project descriptions of the DED and draft project report match.
  • As discussed in the Information for Environmental Documentation section, the potential impacts of each alternative must be analyzed and discussed in the environmental document, along with appropriate minimization, avoidance, and/or mitigation measures.
  • Confirm the project-level conformity status of the project.
  • The technical report and all supporting studies must be completed before the draft project report and DED can circulate.

Project Report

This information should be presented in the Final Environmental Document.

  • Prepare updated air quality report/analysis responding to comments made during DED circulation.
  • Determine whether analysis requires updating to address selected alternative; update if needed.
  • Determine and document whether selected alternative is contained, with substantially the same design concept and scope, in the current conforming RTP and TIP. If RTP and TIP amendments are needed to deal with design concept and/or scope changes during the environmental process, they must be completed and a revised regional conformity determination made by FHWA and FTA before the FED can be signed and a ROD or FONSI issued.
  • Specify and incorporate into the project required avoidance, minimization, and/or mitigation measures for the selected alternative.
  • Provide cost estimates for mitigation measures, as defined, for the Mitigation Cost Tracking System.

Environmental Reevaluation (during Design and Right of Way phases of a project)

Verify adequate progress as specified for Transportation Conformity, that the project remains listed in the RTP and TIP for appropriate work phases, and that regional conformity has not lapsed. "Adequate" progress for conformity purposes is defined in 40 CFR 93 as not more than 3 years elapsing between any of the following milestones: NEPA approval, starting Design work, completing a substantial portion of R/W acquisition, and starting construction.


Local permits and approvals are often required at the construction stage. They are usually the responsibility of the contractor. Where applicable, they should be listed in the PS&E for the project. The Resident Engineer is responsible for ensuring that all air quality permits are complied with during construction.

Here are some typical local permits:

  • In some air districts, an Indirect Source permit or fee may be required for major construction projects.
  • In some air districts, a dust control plan, with plan and inspection fees, may have to be filed for construction activities.
  • Asbestos Notification (for demolition and renovation activities, including removal of asbestos discovered during construction) to the local air district and EPA.
  • Asbestos notification (for naturally occurring asbestos) to the local air district is required where work is in an area that may have it.
  • Local air district permits or formal notification for Portable Equipment to be used during construction. A statewide equipment registration program administered by the California Air Resources Board is available, and is commonly used by contractors and equipment suppliers.
  • If construction includes work subject to Permit to Construct or Permit to Operate requirements under air district rules (such as a stationary engine/generator set, or long-term operation of Portable Equipment like a batch plant), those permits must be obtained prior to starting construction.

Footnotes for the Conformity Flow Chart

  1. The project is located in an attainment/unclassified area for all current federal AQ standards. Therefore, conformity requirements do not apply.
  2. This project is exempt from regional (40 CFR 93.127-128) conformity requirements. Separate listing of the project in the Regional Transportation Plan and Transportation Improvement Program, and their regional conformity analyses, is not necessary. The project will not interfere with timely implementation of Transportation Control Measures identified in the applicable SIP and regional conformity analysis.
  3. The proposed project is fully funded and is in the (INSERT TITLE AND YEAR) Regional Transportation Plan (include amendment number if applicable) which was found to conform by [INSERT METROPOLITAN PLANNING ORGANIZATION (MPO) OR REGIONAL TRANSPORTATION PLANNING AGENCY (RTPA)] on DATE, and FHWA and FTA adopted the air quality conformity finding on DATE. The project is also included in (INSERT MPO OR RTPA) financially constrained YEAR Regional Transportation Improvement Program (include amendment number if applicable), pages #. The (INSERT MPO OR RTPA AND YEAR) Regional Transportation Improvement Program was found to conform by FHWA and FTA on DATE. The design concept and scope of the proposed project is consistent with the project description in the YEAR RTP, the YEAR RTIP and the assumptions in the MPO’S OR RTPA’S regional emissions analysis.
  4. A regional conformity analysis covering the [INSERT NAME OF NONATTAINMENT AREA] for [IDENTIFY POLLUTANT(S) - OZONE AND PM10 ARE THE ONLY POLLUTANTS IN THESE AREAS IN CALIFORNIA AS OF 6/2005] was carried out that includes this project, and all reasonably foreseeable and financially constrained regionally significant projects for at least 20 years from the date that the analysis was started. The analysis used the latest planning assumptions, and the most recent emission models and appropriate analysis methods, as determined by Interagency Consultation on [DATE OF MEETING]. Based on this analysis, the region will be in conformity with the SIP, including this project, based on the [EMISSION BUDGET, PROJECT/NO PROJECT, AND/OR PROJECT/BASELINE] conformity test(s) and analysis procedures, as described in 40 CFR 93.109(l). The design concept and scope of the proposed project is consistent with the project design concept and scope used in the regional conformity analysis. Timely Implementation evaluation reviewed by Interagency Consultation on [DATE OF MEETING].