Publication Detail

Conformity Policy: Air Quality Impact Assessment for Local Transportation Projects


Research Report

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Suggested Citation:
Guensler, Randall L., Susan A. Shaheen, Francisca Mar, Cameron Yee (1998) Conformity Policy: Air Quality Impact Assessment for Local Transportation Projects. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-98-02

This project was undertaken by the Institute of Transportation Studies at Davis (ITS-Davis) for the California Department of Transportation (Caltrans). The Rule's development process has been highly politically charged. ITS-Davis was asked to undertake this project for three reasons to: 1) provide objective opinions from individuals outside the purview of agencies responsible for implementing the Rule; 2) identify and discuss technical issues associated with emissions modeling that should be considered in implementing the Rule; and 3) explore potential institutional conflicts that may arise in implementing the Rule.

The primary goal of the overall project was to develop a conformity modeling protocol for project analysis. The protocol, or guidance document, provides information necessary for an analyst to evaluate the potential air quality impacts of a project in a manner that meets USEPA/Federal Highway Administration (FHWA) approval and is published under separate cover. In preparing the technical modeling protocol, an assessment of the adequacy of emission rate and pollutant dispersion models was undertaken, as well as additional original analyses designed to answer questions that were raised by earlier research efforts at ITS-Davis. The development of the local project carbon monoxide assessment protocol involved numerous separate efforts designed to: 1) identify the regulatory requirements that must be met through modeling procedures; 2) evaluate the predictive capabilities of the emissions impact models that would be applied in meeting the regulatory obligations; and 3) prepare guidance for emissions modelers based upon the review and assessment stages. The final modeling protocol includes guidelines for project description parameters, model selection criteria, data collection, recommended default values, and cautionary notes and advice to analysts. The final modeling protocol is based upon assessment of state-of-the-practice modeling tools and findings related to modeling uncertainty.

However, before the technical modeling guidance document could be developed, the research team undertook a comprehensive review of the Rule and applicable conformity literature to determine where, when, and under what conditions, conformity findings for local projects must be made. This policy document comprises the results of the policy-related research undertaken for project level conformity. A review of the appropriate federal state and local conformity publications, the USEPA's docket of public comments, related environmental regulations, and the project assessment modeling literature was undertaken to identify potential issues that would be addressed in this report.

Report Organization

The first section of this policy document outlines the conformity process and the specific requirements that must be met in making conformity determinations under the CAA and the subsequent conformity rules promulgated by the USEPA and the USDOT.

With the strengthening of the conformity process under the CAA and subsequent final rulemaking by the USEPA and the USDOT, the roles of the federal National Environmental Policy Act (NEPA) and the California Environmental Quality Act (CEQA) in transportation project assessment have also changed. The strengthened link between the conformity process and requirements of NEPA was identified as a critical issue. Given the statutory requirements for conformity process completion, NEPA process completion, and public comment periods, the intent of the Rule appears to encourage project conformity determinations to be made through the NEPA process (and CEQA process in California). The second section of this document addresses NEPA/CEQA requirements and provides guidance that will aid in understanding how the conformity process is interrelated with the environmental impact assessment process. The NEPA/CEQA section explains the environmental assessment process and highlights the relevance of specific conformity requirements in preparing an environmental impact statement (EIS) under NEPA and an environmental impact report (EIR) under CEQA. This section also explains the relationship between the quantitative analysis requirements of NEPA and CEQA and the more specific modeling procedures of the Rule, discussed in the subsequent technical manual. The technical manual highlights the importance of determining the air quality significance of a project and assessing the consistency of the project with regional plans.

The third section of the report addresses the importance of a comprehensive and stringent adherence to the mandates of both the Rule and NEPA/CEQA. The role of public involvement and the specter of citizen suits under the provisions of both the CAA and NEPA/CEQA are discussed. Potential litigation points under the CAA, NEPA, and CEQA are identified and explained. This section also reviews a number of legal cases that appear relevant to CAA conformity determinations and NEPA/CEQA environmental assessments, such as meeting inventory estimates in SIPs and the role of scientific evidence (i.e. modeling results) in litigation. This review indicates when NEPA and CEQA court cases might be referenced by litigants in an effort to counter conformity determinations.

In the final section of this policy report, the findings of the technical modeling studies reported in Guensler, et al. (1994) are summarized: 1) the outputs of the current project assessment models are highly uncertain because the emission rate models were not designed to provide corridor emission rates, and there is inherent uncertainty in the vehicle activity and dispersion model data employed in the analyses; 2) since the model outputs are uncertain, analysts should not conclude that a modeled result, which shows an emission increase or emission decrease associated with a project, is accurate; 3) significant modeling improvements are required if the available project assessment models are to be used to accurately assess project-specific emissions; and 4) a nomagraph system that recognizes model limitations should be prepared for determining when project-level analyses are superfluous under conformity.

This report concludes with a summary of the relevant policy issues associated with project assessment under the Rule. First, the modeling that must be undertaken is identified and framed in terms of the level of accuracy that models can achieve. Second, the importance of undertaking the conformity and NEPA processes concurrently for projects so that statutory requirements can be met on schedule is re-emphasized. Finally, the potential for litigation of conformity findings appears tremendous, indicating that implementing agencies need to work quickly through the public process to develop guidelines (that take into account the capabilities of the existing emission models) for determining when it is reasonable to dispute a conformity determination.