Comparing Actual Environmental Impacts of Projects with Predicted NEPA Environmental Impacts

Focus Area

NEPA Process


Environmental Process






Under 1 year

Research Idea Scope

NEPA environmental documents for projects reflect substantial time and money analyzing and predicting environmental impacts. Decisions on those projects are made based on that information. There is limited or no information regarding the accuracy of NEPA impact predictions when compared with actual project implementation impact outcomes.   For transportation projects, it would be very helpful to know the accuracy of assumptions/ conclusions about some typical analyses (indirect effects, cumulative effects, induced travel, induced growth, stormwater, ecological connectivity). Not only could this information help to identify some analyses that are accurate and resolve/deprioritize some issues that regularly result in controversy between transportation and resource agencies, it could prioritize areas where more work needs to be done.
There is potential for a deviation between predicted and actual environmental impacts if transportation projects change substantially after the NEPA review is completed. In many projects, this is a real possibility; transportation project design usually evolves over a long period of time, yet environmental review is typically conducted at an early stage of design (e.g. 30% design). 
In addition, there appears to be no reliable, consistent or institutionalized process for determining if a project has changed to the degree that the previous conclusions about a project’s impacts, at best, need to be reexamined, and, at worst, are wrong. There is also no data available to tell us if important changes in projects occur without associated NEPA analysis, how often it is happening, and how much of a concern it should be.   Data would help all of us understand if we have a significant flaw in the process or if the issue is nonexistent or relatively minor from the perspective of the environment. If flaws are identified, improvements could provide greater predictability, consistency, and assurances. Increased assurance of a reliable process can reduce efforts to reopen NEPA analysis, reduce conflict and delay, and ensure the expected environmental outcomes occur.
Research Objectives
  • Be able to identify situations and processes when environmental analysis and conclusions for controversial subject areas will be at risk for accuracy. 
  • Be able to identify the degree of concern for identified likely inaccuracies.  
  • Identify risk factors that promote either accuracy or inaccuracy. 
  • Identify if NEPA environmental analysis on alternatives, impact severity, and needed mitigation correlates with the actual, implemented project.   
  • Identify types of significant environmental concerns, if any, associated with project changes post-NEPA.
  • Identify improvements, triggers, risk factors for project changes that should be considered and/or incorporated into the NEPA process.
  • Identify process improvements, if needed, that work for both the applicant transportation agency and the resource agency.
  • Provide a level of assurance to NEPA participants that the process is reliable.
Specific Tasks (if known)
  1. Select 20 completed, major transportation projects that:
    • Involved a new alignment or additional capacity. 
    • Involved some level of concern or controversy regarding at least two of the following: induced travel, induced growth, stormwater, and/or ecological connectivity.  
    • Include a mix of projects – those considered a success by stakeholders and those considered controversial by stakeholders through permitting.
    • Include projects with a “minimum required” NEPA process (scoping and standard EA/DEIS comment points) and an enhanced (e.g. resource agency technical teams) NEPA process.
  1. Evaluate these projects using feedback from transportation project managers and resource technical experts (from transportation and resource agencies).
    • Include review of the NEPA documents and history on project design and description evolution post NEPA
    • Include interviews with applicant teams and resource agency technical staff
  1.  Identify:
    • situations/triggers when additional NEPA has been conducted
    • typical kinds of changes to projects post-NEPA and changes that might warrant more NEPA
    • Percent of times when additional NEPA should have been triggered but wasn’t
    • types of additional NEPA that should have been conducted
    • environmental ramifications of the project changes that were not covered in a NEPA analysis
4. Evaluate the project level NEPA analysis process used, predicted effects and compare them with the actual observable effects of the constructed project for:
  • Indirect effects including induced travel demand and induced growth
  • Cumulative effects
  • Stormwater quality and hydrology
  • Ecological connectivity
5. Determine criteria for determining consistency and inconsistency between predictions and outcomes
  • Identify consistent (and inconsistent) predictions and outcomes.
  • Identify trends or common (risk) factors affecting consistency and inconsistency.
  • Rank the inconsistencies based on the significance of unpredicted impacts.
  • Identify the approaches that provided the greatest degree of consistency between predictions and outcomes (include desirable factors, preferred analyses, or other actions for achieving greater consistency).
6. Suggest triggers or a solution for any identified holes in process. Identify thresholds or a decision tree that assists with determining when project information and detail is appropriate for NEPA analysis. Identify thresholds or a decision tree that assists with determining when additional NEPA should be conducted.

7. Prepare a report compiling information from Tasks 1-6.

Suggested By

Teena Reichgott; NEPA Review Unit, EPA, Region10 Office of Ecosystems, Tribal and Public Affairs

[email protected]