The National Environmental Policy Act (NEPA) was signed into law on January 1, 1970. The Act establishes national environmental policy and goals for the protection, maintenance, and enhancement of the environment and it provides a process for implementing these goals within the federal agencies. NEPA requires federal agencies to consider the potential environmental consequences of their proposals, to consult with other interested agencies, to document the analysis, and to make this information available to the public for comment before the implementation of the proposals.

NEPA is only applicable to federal actions, including projects and programs entirely or partially financed by federal agencies and that require a federal permit or other regulatory decision. Activities that do not require a commitment of federal funds, such as approvals of access controls (e.g., a new interchange) or approval of an airport layout plan, are also federal actions. NEPA does not apply when actions by a state or local government or private entity do not require federal review. In addition, agency inaction, or refusal to take action, is not an action that is subject to NEPA.

While NEPA established the basic framework for integrating environmental considerations into Federal decision-making, it did not provide the details of the process for which it would be accomplished. Federal implementation of NEPA became the charge of the Council on Environmental Quality (CEQ), which interpreted the law and addressed NEPA’s action-forcing provisions in the form of regulations and guidance. In 1978, CEQ issued Regulations for Implementing the Procedural Provisions of the National Environmental Policy Act (40 CFR §§ 1500 -1508). Since that time, CEQ has issued additional guidance and other information covering a variety of issues relevant to the NEPA process. This information is available at

To address the NEPA responsibilities established by CEQ, the Federal Highway Administration (FHWA) and the Federal Transit Administration (FTA) issued regulations (23 CFR § 771), Environmental Impact and Related Procedures. The FHWA guidance complementing the regulations was issued in the form of a Technical Advisory (T.6640.8A), Guidance for Preparing and Processing Environmental and Section 4(f) Documents. The Technical Advisory provides detailed information on the contents and processing of environmental documents. Additional guidance and information on the NEPA process and other environmental requirements are found in the FHWA Environmental Review Toolkit.

The NEPA Process

NEPA directs federal agencies, when planning projects or issuing permits, to conduct environmental reviews to consider the potential impacts on the environment by their proposed actions.

For transportation projects, NEPA requires the FHWA and other transportation agencies to consider potential impacts to the social and natural environment. In addition to evaluating the potential environmental effects, FHWA must take into account the transportation needs of the public in reaching a decision that is in the best overall public interest. (23 USC 109(h))

The NEPA statute and implementing regulations set forth a process to evaluate potential impacts as well as requirements for documentation of decisions resulting from that process. The key elements of the process include determining the project’s purpose and need and the range of alternatives to be considered; determining potential environmental impacts; coordinating with relevant agencies; involving the public; determining mitigation for unavoidable impacts; and documentation of the analysis and decisions through an environmental impact statement, an environmental assessment, or a categorical exclusion supported by the administrative record.

NEPA Process and Documentation Options

There are three processing and environmental documentation options under NEPA, depending on whether or not an undertaking significantly affects the environment. These three options include: categorical exclusion (CE); environmental assessment (EA); and environmental impact statement (EIS). The process for environmental documentation under NEPA is summarized in the chart below:

Categorical Exclusions

Under NEPA, transportation projects that do not individually or cumulatively have significant environmental effects are classified as categorical exclusions (CEs). The purpose of a CE is to reduce paperwork and delay by providing a compliance mechanism where an EA or EIS is not obviously necessary. Research has indicated that approximately 92 percent of the projects processed by state transportation agencies and the FHWA are CEs.

Each individual federal agency has regulations that implement NEPA. The CEQ regulations require these agencies’ regulations to include a list of specific classes or types of actions that qualify as CEs.

FHWA’s and FTA’s NEPA regulations, titled Environmental Impact and Related Procedures, include two general types of CEs. Regulations at 23 CFR 771.117(c) provide a listing of types of common highway- and transit-related actions found to meet CEQ’s CE requirements.

Experience has shown that these actions never or almost never cause significant environmental impacts. These actions normally do not require any further NEPA approvals by FHWA or FTA.

The FHWA/FTA regulations at 23 CFR 771(d) list another examples of actions that may be considered CEs, if approved by FHWA/FTA. The regulations state that this list is not all-inclusive. 23 CFR 771.117(d) allows additional actions that are found to meet CEQ’s CE requirements to be designated as CEs upon the submission of documentation to FHWA or FTA which demonstrates that the specific conditions or criteria for those CEs are satisfied and that significant environmental impacts will not result.

The CEQ regulations require an agency’s regulations to provide for unusual circumstances under which a normally excluded action may have a significant effect. In cases of unusual circumstances, appropriate environmental studies are needed to determine if a CE classification is appropriate. FHWA and FTA define these unusual circumstances as:

      • Significant environmental impacts
      • Substantial controversy on environmental grounds
      • Significant impact on Section 4(f) and Section 106 properties
      • Inconsistencies with any Federal, State, or local environmental requirements

Environmental Assessments

Where the significance of environmental impacts are unknown, a federal agency may prepare an environmental assessment (EA) to determine whether or not an environmental impact statement (EIS) is necessary (i.e. the action would significantly affect the environment.) If the answer is no, the agency issues a finding of no significant impact (FONSI). The FONSI may address measures that an agency will take to reduce (mitigate) potentially significant impacts. If it is determined that the environmental consequences of a proposed federal undertaking are significant, an EIS will then be prepared.

Approximately seven percent of state DOT projects are processed with EAs. An EA is a concise public document designed to provide sufficient evidence and analysis to assist in determining the significance of the environmental impacts of a transportation project proposal. An EA may also facilitate the preparation of an EIS when one is necessary.

EA documents typically include brief discussions of the need for the proposal; evaluation of any alternatives to the proposal, environmental impacts of the proposed action and the alternatives, and a listing of agencies and persons consulted during the preparation of the EA.

FHWA and FTA must approve an EA before it is made available to the public. EAs do not need to be circulated, but they must be made available to the public through notices of availability in local, state, or regional clearinghouses, newspapers and other means. Depending on the FHWA-approved state public involvement procedures, a public hearing may or may not be required. A 30-day review period is required but may be reduced in rare circumstances.

After public comments are received and considered, a determination of the significance of the impacts is made. If after completing the EA it is evident that the proposed action will have no significant impact on the environment, a finding of no significant impact (FONSI) is prepared and no EIS is required. If at any point in the process it is evident that there may be a significant environmental impact, the first steps to preparing an EIS are immediately taken.

A FONSI is a document that briefly explains why the project will have not have significant impacts (i.e., it explains why no EIS is being prepared). The FONSI must include the EA modified to reflect all applicable comments and responses (or incorporate it by reference) or include a summary of it and must note any other documents related to the EA. If not done in the EA, the FONSI must include the selected alternative. No formal public circulation of the FONSI is required, but the state clearinghouse must be notified of the availability of the FONSI. In addition, FHWA recommends that the public be notified through notices in local newspapers.

Environmental Impact Statements

NEPA requires federal agencies to prepare environmental impact statements (EISs) when there is a proposal for a major federal action that significantly affects the quality of the human environment. Only a very small number of projects processed by state transportation agencies require EISs. An EIS includes a detailed evaluation of the proposed action and alternatives. The public, other federal agencies and outside parties may provide input into the preparation of an EIS and then comment on the draft EIS when it is completed. After a final EIS is prepared and at the time of its decision, a federal agency will prepare a public record of its decision addressing how the findings of the EIS, including consideration of alternatives, were incorporated into the agency’s decision-making process. The purpose of an EIS is to serve as a tool to promote environmentally sensitive decisionmaking. To accomplish that goal, the document should:

      • Inform the decision maker of the environmental effects of an agency action;
      • Make agencies consider alternative ways of taking actions that would avoid or minimize adverse impacts; and
      • Inform the public.

An EIS should also:

      • Be analytic rather than encyclopedic;
      • Be clear, concise and to the point;
      • Discuss briefly, non-important issues; and
      • Incorporate material by reference.

The key steps in the EIS process are completed in the following order:

      • Notice of Intent (NOI),
      • Scoping,
      • Draft EIS,
      • Final EIS,
      • Record of Decision (ROD).

Notice of Intent and Scoping

The Notice of Intent (NOI) to prepare an EIS is published in the Federal Register by the lead Federal agency. The purposes of the NOI are to notify and involve all agencies and individuals about the proposed action and to identify the issues that should be analyzed and eliminate from study those that are not important to the decision. The content of a NOI typically consists of a brief description of the proposed action, possible alternatives, and the proposed scoping process. Scoping is an early and open process involving the public and other federal, state, and local agencies, as well as Indian tribes, for determining the scope of issues to be addressed in the EIS, identifying alternatives, and identifying the significant issues relating to the project. (i.e., to narrow the focus of the analysis).

FHWA’s Technical Advisory (T.6640.8A), Guidance for Preparing and Processing Environmental and Section 4(f) Documents provides additional guidance on the preparation of the NOI and on the scoping process.

Draft EIS and Final EIS

The draft EIS provides a detailed description of the proposal, the purpose and need, reasonable alternatives, the affected environment, and presents an analysis of the anticipated beneficial and adverse environmental effects of the alternatives. If there is a preferred alternative, it can be identified at the draft EIS stage and it must be identified at the final EIS stage. Once the draft EIS is prepared and it is approved, agencies must:

      • Circulate it to all relevant federal, state, and local agencies,
      • Make available to the public,
      • Submit the document to the Environmental Protection Agency for publishing the notice of availability of the draft EIS for public comment in the Federal Register and

The usual comment period on a draft EIS is not less than 45 days and no more than 60 days, and unless (1) a different period is set by agreement of the lead agency, project sponsor, and all participating agencies, or (2) the deadline is extended by the lead agency “for good cause.” All dates are measured from the date of public notice by EPA in the Federal Register.

Following a formal comment period and receipt of comments from the public and other agencies, the final EIS is prepared. The final EIS includes responses to any issues raised by the comments on the draft EIS. Based on analysis and comments, the final EIS must identify the preferred alternative even if it is already identified in the draft EIS. After responding to comments, the agency must circulate the final EIS for review. Agencies cannot make a final decision until 30 days after the final EIS is filed.

Record of Decision (ROD)

The ROD is the final step in the EIS process. In accordance with the CEQ regulations, FEIS and ROD documents are issued as separate documents with a minimum 30-day period between the FEIS and ROD. Section 1319(b) of MAP-21 directed the lead agency, to the maximum extent practicable, to combine the final EIS (FEIS) and ROD into a single document unless:

      • The FEIS makes substantial changes to the proposed action that are relevant to environmental or safety concerns; or
      • There are significant new circumstances or information relevant to environmental concerns and that bear on the proposed action or the impacts of the proposed action.

Reevaluations and Supplemental EISs


A reevaluation is an analysis of any changes in a proposed action, affected environment, anticipated impacts, and mitigation measures at specific times in the project development process. The purpose of a reevaluation is to determine whether an approved environmental document or CE designation remains valid and to determine whether significant changes require preparation of a supplemental or new environmental document. Formal documentation of the reevaluation process on the validity of the approved EIS, FONSI or CE designation is not necessary in all cases, but consultation with FHWA is required before major approvals (e.g., right-of-way authorization or construction authorization). In cases of a draft EIS, where a final EIS has not been issued and where no action to advance the project has occurred in the last three years, 23 CFR 771.129 requires a written reevaluation of the determination that the original document is still valid and formalizes the consultation between FHWA and a state DOT. A final EIS is considered valid up to three years following the last major approval. If no action to advance a project has occurred in the last three years, a written reevaluation is required. Project-specific issues related to reevaluation should be referred to the appropriate FHWA division office.

Supplemental EISs A draft EIS or final EIS may be supplemented if the reevaluation of the EIS reveals that:

      • There are significant changes in the proposed action that are relevant to the environmental concerns, or
      • There are significant new circumstances that are relevant to the proposed action or its impacts, or
      • There is significant new information that is relevant to the proposed action or its impacts.

An agency is not required to develop a new or supplemental EIS every time it receives new information or a change is made regarding a project. For example, a supplemental EIS is not required if changes or new information/circumstances do not result in previously unidentified significant adverse impacts or if they reduce the adverse environmental impacts without additional new significant impacts. The format of a supplemental EIS is flexible (i.e., it does not have to follow the standard CEQ format for EISs). Generally, a supplemental EIS will:

      • Tell why a supplemental EIS was prepared;
      • Summarize or reference the valid part of original EIS; and
      • Evaluate changes/new impacts.

Early coordination with involved agencies and the public is essential, although scoping is not required. A supplemental EIS of limited scope does not necessarily rescind previous project approvals or affect project activities. On the other hand, a supplemental EIS of major scope will require suspension of some or all project activities.

Key Components of the NEPA Process

Purpose and Need

The purpose and need discussion is one of the most important parts of any NEPA process and should, therefore, be clear and well documented. It should be a full and honest explanation of why an agency is considering an action. The purpose and need is a statement of the problem and evidence that supports that the problem exists.

Some common needs included in a purpose and need discussion are transportation demand, safety, legislative direction, urban transportation plan consistency, modal interrelationships, system linkage, and the condition of an existing facility.

Since the purpose and need discussion is essential to the development of the range of alternatives, it should include a clear statement of identified objectives that the proposed action is intended to achieve for improving transportation conditions. Some goals in a purpose and need discussion may include: achieving an objective in a transportation plan; supporting local land use and growth objectives, or serving national defense or security needs.

The lead agencies are responsible for the development of the proposed action’s purpose and need discussion. In developing the statement of purpose and need, in the case of an EIS, the lead agencies must provide opportunities for the involvement of participating agencies and the public and must consider the input provided by these groups. After considering this input, the lead agencies decide the project’s purpose and need. Per guidance issued by CEQ, which was affirmed by Congress in its conference report on SAFETEA-LU, other Federal agencies should afford substantial deference to FHWA’s or FTA’s purpose and need for a proposed transportation action.

Additional information is available on FHWA’s Environmental Review Toolkit web page under NEPA and Transportation Decisionmaking, Elements of Purpose and Need. Also see FHWA and FTA’s 2003 Guidance on Purpose and Need and the AASHTO Practitioner’s Handbook, Defining the Purpose and Need and Determining the Range of Alternatives for Transportation Projects.

Alternatives Analysis

The alternatives analysis describes the process that was used to develop, evaluate, and eliminate potential alternatives based on the purpose and need of the project. In accordance with the requirements of 23 CFR 771.111(f), project alternatives must connect logical termini, have independent utility, and not restrict the consideration of future transportation alternatives. The analysis of alternatives is a basic requirement of NEPA. It explains to the public the options that are available to the agency in addressing the problem identified in the purpose and need. Federal agencies are not required to consider every potential alternative; however, they are responsible for developing the full range of alternatives. In the case of an EIS, the lead agencies must provide opportunities for the involvement of participating agencies and the public in developing the alternatives and must consider the input provided by these groups. After considering this input, the lead agencies will decide the range of alternatives for analysis. The alternatives section of an EIS should present the environmental impacts of a proposed action and all reasonable alternatives at a comparable level of detail and in comparative form to give the decisionmaker a clear basis for choice among options. The “no-build” alternative is included as a benchmark against which the impacts of other alternatives can be compared.

If there is a preferred alternative, an agency can identify it at the draft EIS stage and must identify it at the final EIS stage and the basis for that decision. SAFETEA-LU allows the preferred alternative in an EIS to be developed to a higher level of detail than the other alternatives in order to facilitate the development of mitigation measures or facilitate concurrent compliance with other applicable environmental laws.

Additional information is available on FHWA’s Environmental Review Toolkit web page under NEPA and Transportation Decision-making, Development and Evaluation of Alternatives.

Impacts and Mitigation

NEPA requires consideration of the direct, indirect, and cumulative impacts of a proposed action and its alternatives on the environment. Direct effects are those that are caused by the action and occur at the same time and place. Indirect effects are those that are caused by the action and occur later or farther away (off-site) but are still reasonably foreseeable. Cumulative impacts are defined as the impact on the environment that results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (federal or non-federal) or person undertakes such actions. Potential measures to mitigate adverse environmental effects also must be considered. Section 1508.20 of CEQ’s Regulations defines mitigation as including:

      • Avoiding the impact altogether by not taking a certain action or parts of an action.
      • Minimizing impacts by limiting the degree or magnitude of the action and its implementation.
      • Rectifying the impact by repairing, rehabilitating, or restoring the affected environment.
      • Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action.
      • Compensating for the impact by replacing or providing substitute resources or environments.

Typically, in cases of an EIS, the draft EIS describes options for mitigation, while the final EIS includes the decisions on what mitigation would be implemented.

Interagency Coordination

The NEPA process includes requirements for interagency coordination and cooperation and public participation in planning and project development decisionmaking.

CEQ’s regulations introduced the concepts of “lead agency” and “cooperating agency” to help streamline the environmental process; eliminate duplication in Federal, state, and local procedures; and integrate NEPA requirements with other Federal environmental review and consultation requirements. A lead agency (40 CFR 1508.16) is defined as the agency preparing or having taken primary responsibility for preparing the EIS and for supervising the NEPA process. The U.S. DOT is designated as the lead agency for the environmental review process for any highway or transit project requiring U.S. DOT approval. FHWA is the federal lead agency in the NEPA process for highway projects requiring FHWA approval. FTA fulfills that role for transit projects. A cooperating agency (40 CFR 1508.5) is an agency with jurisdiction by law or special expertise on any environmental issues that the EIS discusses.

The direct recipient of federal funds for a project must serve as a joint lead agency. For FHWA, the state DOT is typically the direct recipient of project funds and, therefore, must serve as a joint lead agency along with FHWA. For FTA, the local transit agency typically is the direct recipient of project funds, and therefore serves as a joint lead agency along with FTA. In addition to the required lead agencies, other Federal, state, or local governmental entities, may act as joint lead agencies, at the discretion of the required lead agencies, in accordance with CEQ Regulations. Private entities, either acting as sponsors or co-sponsors of projects, cannot serve as joint lead agencies, and their role is limited to providing environmental or engineering studies and commenting on environmental documents.

The lead federal agency works cooperatively with other federal and state agencies during the environmental review process. Lead agency responsibilities in the NEPA process include, where applicable, inviting cooperating agencies, scoping, providing project information, conducting field reviews, developing consensus among a wide range of stakeholders with diverse interests, resolving conflict, and ensuring that issues are addressed and decisions are fully explained in the environmental document.

The concept of “cooperating agencies” is a mechanism designed to address agencies’ concerns early in the NEPA process and avert late disagreements. Cooperating agencies are agencies with jurisdiction by law over a project and/or special expertise on environmental issues that the EIS discusses. These agencies include, but are not limited to:

      • U.S. Army Corps of Engineers [Section 10/404 Permits]
      • U.S. Fish and Wildlife Service
      • U.S. Environmental Protection Agency
      • National Park Service [Section 6(f)]
      • U.S. Coast Guard [Section 9 Permits]
      • Advisory Council on Historic Preservation [Historic/Archaeological Sites]
      • State and local agencies
      • Indian Tribes

Cooperating agency responsibilities include participating in scoping, attending joint field reviews, and providing meaningful and early input to issues of concern. SAFETEA-LU created a new category of “participating agencies” to allow more agencies a formal role and rights in the environmental review process. Federal state, tribal, regional, and local government agencies that may have an interest in the project should be invited to serve as participating agencies. Nongovernmental organizations and private entities cannot serve as participating agencies. All cooperating agencies are participating agencies, but not all participating agencies are cooperating agencies. SAFETEA-LU also required that the lead agencies establish a plan for coordinating public and agency participation and comment during the environmental review process. These new requirements are discussed in more detail in the subsection below titled SAFETEA-LU Environmental Review Provisions.

Additional information is available on FHWA’s Environmental Review Toolkit under NEPA and Transportation Decisionmaking, Interagency Coordination.

Public Involvement

Handled correctly, scoping and public participation in the NEPA process will improve acceptance of the decision and, at minimum, provide the decisionmaker with the best information possible for making a decision. The amount and type of public involvement will vary depending on the complexity and degree of controversy involved in a project. It is very helpful to obtain public input on a range of issues, including scoping; purpose and need; alternative development; effects analysis; making the decision; and implementation.

SAFETEA-LU requires that the lead agencies establish a plan for coordinating public and agency participation and comment during the environmental review process. Coordination plans are discussed further in the subsection titled SAFETEA-LU Environmental Review Provisions.

AASHTO Practitioner’s Handbook 05—Utilizing Community Advisory Committees for NEPA Studies (December 2006) suggests a Citizen Advisory Committee as a public participation technique that can be employed to gain stakeholder feedback, identify and resolve local concerns, and build community support during the pre-NEPA and NEPA decision-making processes.


The draft EIS must summarize the scoping process, the results of any meetings that have been held, and any comments received during preliminary coordination. Between the draft EIS and the final EIS, the state DOT and FHWA must consider and respond to all substantive comments received on the draft EIS, including those from public hearings.

Comments received after the close of the comment due date should be considered, if at all possible. The final EIS should note that the comments were filed late but were treated consistent with NEPA. Courts have ruled that the views of the cooperating agencies regarding the environmental impacts of a project are entitled to deference from the lead agency. However, this does not mean that the comments of such agencies must be substituted for reasonable, good faith judgments of the lead agency. The ultimate decision under NEPA rests with the lead agency. The administrative record for the final EIS must include copies of the comments received and the agency’s responses. If the EIS was changed in response to comments, these changes should be referenced in the responses.

AASHTO Practitioner’s Handbook 02—Responding to Comments on an Environmental Impact Statement, contains more information about this topic.

Implementing Quality NEPA Documents

The traditional format for EIS documents is described in CEQ regulations (40 CFR 1502) and in FHWA’s Technical Advisory T 6640.8A, Guidance for Preparing and Processing Environmental and Section 4(f) Documents (TA).

Since 2006, several efforts have been undertaken to improve the quality of NEPA documents, many of which had become overly lengthy and cumbersome. These efforts stressed that EISs should be clear, concise, and easy to understand. In a 2006 memorandum, FHWA endorsed this approach as consistent with FHWA guidance and CEQ regulations (FHWA Memorandum: Improving the Quality of Environmental Documents, July 31, 2006). The agency urged practitioners take advantage of the regulations’ flexibility and improve the effectiveness of NEPA documents.

In 2014, AASHTO issued a Practitioner’s Handbook on Preparing High-Quality NEPA Documents and related Examples of Effective Techniques for Preparing High-Quality NEPA Documents to help advance the state of the practice on NEPA documentation.

In general, a high-quality NEPA document is one that:

    • Is readily understandable by all audiences, including those without technical expertise;
    • Provides key information in an easy-to-navigate format;
    • Focuses on pertinent information and avoids unnecessary bulk;
    • Includes supporting technical information in appendices; and
    • Meets all legal requirements.

SAFETEA-LU and MAP-21 Environmental Review Provisions

The term “environmental review process” refers to the project development process followed when preparing a NEPA document for a transportation project. In addition to NEPA requirements, the term also includes the process for compliance with, and completion of, any environmental permit, approval, review, or study required for the transportation project under any Federal law. Some of the other Federal environmental laws, such as Section 4(f) of the Department of Transportation Act, are within the purview of USDOT, and some, such as Clean Water Act Section 404 permitting, are under the authority of other Federal agencies.

In 2005, the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) was signed into law. Section 6002 of the law established procedures that must be followed when preparing an EIS for a highway, transit, or multimodal projects. These changes are aimed at improving and streamlining the environmental review process for these transportation projects. These changes, however, came with some additional steps and requirements. For an archived summary of the SAFETEA-LU provisions previously posted on this website, link here.

The Moving Ahead for Progress in the 21st Century Act (MAP-21) was signed into law and took effect in 2012. Subtitle C of Title I of MAP-21 includes 23 separate provisions related to accelerating project delivery for highway and transit projects. These provisions touch on many aspects of project delivery, from transportation planning to environmental review to procurement. For more details, link to the AASHTO MAP-21 Resource Center.

Resources on implementation of SAFETEA-LU and MAP-21 environmental review provisions are provided on FHWA’s Environmental Review Toolkit under Highlights of Environmental Provisions and on the FHWA MAP-21 website.

Indirect Effects/Cumulative Impacts

This section provides a brief overview of secondary/indirect and cumulative impacts and related requirements as they affect the transportation community. Topics include the following:


The Federal Highway Administration and other federal agencies’ responsibility to address and consider direct, indirect, and cumulative impacts in the National Environmental Policy Act (NEPA) process was established in the Council on Environmental Quality (CEQ) Regulations for Implementing the Procedural Provisions of the National Environmental Policy Act (40 CFR §§1500-1508).

The CEQ regulations define the impacts and effects that must be addressed and considered by federal agencies in satisfying the requirements of the NEPA process. Direct, indirect and cumulative impacts can be defined as follows:

    • Direct effects are caused by the action and occur at the same time and place. (40 CFR § 1508.8)
    • Indirect effects are caused by the action and are later in time or farther removed in distance, but are still reasonably foreseeable. Indirect effects may include growth inducing effects and other effects related to induced changes in the pattern of land use, population density or growth rate, and related effects on air and water and other natural systems, including ecosystems. (40 CFR § 1508.8) Indirect effects and secondary effects are used interchangeably by FHWA.
    • Cumulative impact is the impact on the environment, which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (Federal or non-Federal) or person undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time. (40 CFR § 1508.7)

According to FHWA guidance, the determination or estimation of future impacts is essential to both indirect and cumulative impact analysis. However, the focus must be on reasonably foreseeable actions, those that are likely to occur or probable, rather than those that are merely possible.

For additional information on indirect/secondary and cumulative impacts for transportation projects, please see the question-and-answer guidance document, FHWA Interim Guidance: Indirect and Cumulative Impacts in NEPA [DOC 186kb].

Indirect Effects

Indirect effects (effects caused by the project, but occurring later in time or farther removed in distance than direct impacts) include changes in land use attributable to the project (induced growth) and impacts on environmental resources that occur as a result of the project’s influence on land use. Besides induced growth and related effects, the definition of indirect effects also includes other potential environmental impacts caused by a project, such as the effect of habitat fragmentation on species viability over time or changes in wetland functions due to stormwater runoff.

Induced Growth and Land Use Change

Transportation projects often reduce travel time, enhancing the attractiveness of surrounding land for development through changes in accessibility. These changes in accessibility may influence development in a localized area adjacent to the transportation project (e.g. gas stations and motels near an interchange), as well as larger-scale effects on the location of future development within a region. However, transportation projects are only one of numerous factors that influence development patterns. Other important factors include land availability and prices, economic conditions, political and regulatory conditions, and the quality of public services. The estimation of induced growth effects requires the identification of the project contribution to changes in development patterns. Once the project effect on land use has been identified, this information can be used to estimate the environmental impacts attributable to land use changes caused by the project, such as habitat fragmentation or stormwater runoff effects on water quality.

Methods for analyzing induced growth effects of transportation projects include quantitative methods, such as travel demand models and integrated land use and transportation models, and qualitative methods such as scenario writing, Delphi Technique, and expert panels.

Cumulative Impacts

According to the FHWA’s Interim Guidance: Questions and Answers Regarding the Consideration of Indirect and Cumulative Impacts in the NEPA Process (2003), cumulative impacts include the total of all impacts to a particular resource that have occurred, are occurring, and will likely occur as a result of any action or influence, including the direct and reasonably foreseeable indirect impacts of a Federal activity. According to the guidance:

“Cumulative impact analysis is resource specific and generally performed for the environmental resources directly impacted by a Federal action under study, such as a transportation project. However, not all of the resources directly impacted by a project will require a cumulative impact analysis. The resources subject to a cumulative impact assessment should be determined on a case-by-case basis early in the NEPA process, generally as part of early coordination or scoping.”

CEQ guidance titled Considering Cumulative Effects Under the National Environmental Policy Act identifies four basic types of effects that can lead to cumulative impacts:

    • Type 1: Repeated additive effects on a resource from a single project.
    • Type 2: Stressors from a single project that have interactive (countervailing or synergistic) net effect on a resource.
    • Type 3: Additive effects on a resource arising from multiple sources (projects, point sources, or general effects associated with development).
    • Type 4: Effects arising from multiple sources that affect resources in an interactive fashion.

Cumulative impact analysis requires careful development of the no build alternative scenario to include reasonably foreseeable future actions. Coordination with agency and local officials is an important part of identifying other projects that should be included as part of the no build alternative.

CEQ guidance identifies methods for analyzing cumulative effects, including: questionnaires, interviews and panels, checklists, matrices, networks and system diagrams, modeling, trends analysis, overlay mapping and geographic information systems, carrying capacity analysis, ecosystem analysis, economic impact analysis and social impact analysis.

The Indirect Effects and Cumulative Impacts Analysis Process for Transportation Projects

Separate analyses should be conducted to evaluate indirect effects of transportation projects and to evaluate project-related cumulative impacts. However both processes should include consultation with stakeholders and the public, identification of important trends and issues, and analysis of the potential for land use change and related environmental impacts on valued and vulnerable resources.

As summarized below, the National Cooperative Highway Research Program (NCHRP) has provided a detailed step-by-step approach for conducting indirect effect assessment, and the CEQ guidance outlined steps for cumulative impact assessments.

Indirect Effects Analysis

Specifically, for evaluating indirect effects, NCHRP Report 466: Desk Reference for Estimating the Indirect Effects of Proposed Transportation Projects presents the following eight-step process:

      • Step 1 – Define the Study Area Boundaries. The purpose of Step 1 is to set appropriate study area boundaries for the analysis of indirect effects as well as the timeframe for the analysis.
      • Step 2 – Identify the Study Area Communities’ Trends and Goals. The purpose of Step 2 is to gather information on community trends and goals in the study area, focusing on socioeconomic and land use issues.
      • Step 3 – Inventory Notable Features. The purpose of Step 3 is to identify specific valued, vulnerable or unique elements of the natural environment that will be analyzed in the assessment of indirect effects.
      • Step 4 – Identify Impact Causing Activities of the Proposed Action and Alternatives. The purpose of Step 4 is to identify the cause and effect relationships between the transportation project and potential impacts that may come into conflict with the goals identified in Step 2 or the notable features identified in Step 3.
      • Step 5 – Identify Potential Impacts For Analysis. The purpose of Step 5 is to compare the impact-causing activities developed in Step 4 with the inventory of goals, trends and notable features that make up the baseline conditions identified in Steps 2 and 3.
      • Step 6 – Analyze Impacts. The purpose of Step 6 is to determine the magnitude and location of the potential impacts identified in Step 5.
      • Step 7 – Evaluate Analysis Results. The purpose of Step 7 is to evaluate the uncertainties in the methodology used to evaluate impacts, in order to better understand the analysis results.
      • Step 8 – Assess Consequences and Develop Mitigation. The purpose of Step 8 is to assess the consequences of the impacts and to develop strategies to address unacceptable impacts, which occur when an impact identified in Step 6 conflicts with a goal identified in Step 2 or with a notable feature identified in Step 3.
Cumulative Impact Assessment

Although not specific to transportation projects, CEQ provides the following 11-step process for cumulative impact assessment in the report Considering Cumulative Effects Under the National Environmental Policy Act:

      • Step 1 – Identify the significant cumulative effects issues associated with the proposed action and define the assessment goals.
      • Step 2 – Establish the geographic scope for the analysis.
      • Step 3 – Establish the time frame for the analysis.
      • Step 4 – Identify other actions affecting the resources, ecosystems, and human communities of concern.
      • Step 5 – Characterize the resources, ecosystems, and human communities identified during scoping in terms of their response to change and capacity to withstand stresses.
      • Step 6 – Characterize the stresses affecting these resources, ecosystems, and human communities and their relation to regulatory thresholds.
      • Step 7 – Define a baseline condition for the resources, ecosystems, and human communities.
      • Step 8 – Identify the important cause and-effect relationships between human activities and resources, ecosystems, and human communities.
      • Step 9 – Determine the magnitude and significance of cumulative effects.
      • Step 10 – Modify or add alternatives to avoid, minimize, or mitigate significant cumulative effects.
      • Step 11 – Monitor the cumulative effects of the selected alternative and adapt management.

The NCHRP and CEQ approaches involve overlapping steps that can be conducted concurrently and support both indirect effect and cumulative impact processes, such as establishing the boundary and baseline conditions and trends for the resources of concern. However, care should be taken when documenting the IECI assessment results in the environmental assessment or environmental impact statement to clearly differentiate between indirect effects and cumulative impacts and, thereby, ensure that both topics are sufficiently addressed. One way to do this is to discuss indirect effects and cumulative impacts in separate sections within a single chapter, or as separate chapters (See Case Studies- St. Croix River Crossing Supplemental Final Environmental Impact Statement (SFEIS)), to make sure that each can stand on its own as a hard look at the pertinent issues.

Generally, the resources of concern for cumulative impact evaluation are those for which the project has the potential to directly or indirectly effect. Both the NCHRP and CEQ methodologies allow for either quantitative, e.g., analytical model, or qualitative, e.g., expert panel, analysis of the magnitude of the effects on the resources of concern. For complex projects, it is often advisable to employ more than one analysis tool to improve the confidence in the analytical results and/or to reveal a range of results.