Transportation projects have both direct and indirect effects on the environments in which they are located. The National Environmental Protection Act (NEPA) and its implementing regulations mandate the assessment and disclosure of reasonably foreseeable effects of transportation projects. As a result, procedures have been established to identify and estimate many of the direct effects of projects. However, the indirect effects are both harder to identify and more difficult to assess. These indirect effects include, but are not limited to, changes in social and economic conditions, natural resources, cultural/historical resources, accessibility, induced traffic, noise levels, and air quality.

The NEPA Implementing Regulations (40 CFR 1502.16 (b)) require the scientific analysis of indirect effects and their significance as part of the environmental impact review process. Federal Highway Administration (FHWA) regulations do not specifically address the analysis of indirect effects, but refer to the NEPA Implementing Regulations. However, FHWA Technical Advisory T 6640.8A, Guidance for Preparing and Processing Environmental Section 4(F) documents more specifically requires the evaluation of indirect social, economic, and environmental effects. Other federal and state agencies also have requirements related to indirect effects that must be addressed as well.

State DOTs and other agencies have expressed a need for guidance in estimating the indirect effects of proposed projects. Hence, research is needed to accomplish the following: define indirect effects of proposed projects, develop techniques for identifying, understanding, describing, and estimating these effects, and prepare guidelines to facilitate the analysis of indirect effects of transportation projects.

The objective of this research is to develop an analysis framework and supporting methods to facilitate identifying, understanding, describing, and evaluating indirect effects of transportation projects. Specifically, this research will accomplish the following: (1) establish a working definition of indirect effects, which includes an interpretation of reasonably foreseeable effects; (2) identify and describe the causal relationships among projects, indirect effects, and the conditions under which they are likely to occur; (3) identify and assess the adequacy of current procedures and techniques for estimating indirect effects; and (4) recommend a framework for reviewing transportation projects for indirect effects, with appropriate processes for separating project-induced effects from those that would occur without the project. The research is expected to produce a set of guidelines for use in analyzing the indirect effects of transportation projects.

To accomplish the project objective, the following tasks are envisioned: (1) Establish a working definition of indirect effects of transportation projects. This definition should be based on the NEPA regulations, the literature, and contacts with agencies involved in transportation planning and development and in environmental monitoring and regulation. A critical element will be to establish guidance for transportation agencies in determining the spatial and temporal bounds of a reasonably foreseeable future. Proposals should describe the process that will be used to undertake this task. (2) Catalog adverse, beneficial, and nonimpacting indirect effects associated with different types of transportation projects. The indirect effects need to be categorized to reflect the differences in scale between systemwide transportation plans and specific projects. Identify and describe the causal relationships among projects, indirect effects, and the conditions under which they are likely to occur. In this effort, the procedures and techniques that have been applied to estimate indirect effects should be cataloged. Information should be gathered from published literature, environmental documents, and contacts with transportation, regulatory, academic, and other organizations. (3) Evaluate the procedures and techniques for estimating the indirect effects identified in Task 2. Document the sources of data, the analysis techniques or methods used, and the applicability of the methods. Critique the techniques and procedures based on practicality, reliability, cost, and acceptability. Conceptualize other tools to aid the analysis process and describe these in sufficient detail to permit their development in Task 8 or subsequent research. (4) Propose a preliminary framework for the systematic analysis of indirect effects of transportation projects. The framework should incorporate processes (guidance) for establishing the spatial and temporal limits of project impacts and for separating project-induced effects from those that would have occurred without the project. The framework should reflect the roles of different agencies in the analysis and mitigation of indirect effects. Develop checklists, flow charts, or other tools to facilitate the application of the framework. The proposal should include the proposer's current thinking on the nature of the framework and examples of how it would be applied. (5) Prepare a draft interim report describing the following: (a) the established working definition for indirect effects; (b) the proposed framework, supporting rationale, and associated checklists, flow charts, or other aids; (c) the techniques and procedures for estimating indirect effects to be used within the framework; (d) the recommendations for tools that need to be obtained or developed to support the analysis process (i.e., toolbox); (e) the types of case studies that would be used to demonstrate the applicability of the process; and (f) the plans for packaging the framework and associated methodologies into a set of guidelines. The interim report should also indicate areas where the analysis of indirect effects is not possible without further research. The panel will review the interim report and determine whether there is merit in proceeding to actual development of the guidelines. The contractor will be expected to participate in an interim meeting with the project panel to set directions for completion of study. The contractor will not proceed with Task 6 without NCHRP approval. (6) Prepare a revised version of the interim report reflecting the comments of the panel. Provide 50 copies of this version for an extended review of the proposed analysis framework by professionals in the transportation and environmental fields. The NCHRP will distribute the report and compile all review comments received. The contractor will review the comments and recommend changes to the analysis framework and supporting methodologies. The contractor should be prepared to meet with the panel to determine which changes will be incorporated into the proposed guidelines. (7) Finalize the framework and associated procedures and techniques as approved in Task 6. Compile draft guidelines documenting the various indirect effects, indicating when they should be estimated, and describing the techniques that can be used to estimate them. Develop tools and aids approved by the project panel and package the guidelines into a document that will facilitate their use. (8) Demonstrate the applicability of the analysis framework by undertaking several case studies. Select case studies that represent various types of transportation improvements and environmental situations (e.g., urban, suburban, and rural areas). Estimate indirect effects using guidelines developed in Task 7 by applying them to actual projects approved by the project panel. Modify the draft guidelines based on the results of this effort and project panel review. (9) Prepare a final report documenting the entire research effort. The final report should include the following: (a) an executive summary describing indirect effects, the analysis framework, and the procedures for estimating indirect effects; (b) a revised set of guidelines for analyzing indirect effects; (c) documentation for any items to be included in the toolbox; (d) other necessary supporting materials; (e) a recommended implementation plan for moving the results of this research into practice; and (f) a summary of future research needs.

Status: The project has been completed.

Report Availability: The report has been published as NCHRP Report 403, "Estimating the Indirect Effects of Proposed Transportation Projects" and is available through NCHRP.