## Facts

- The Clean Air Act Amendments of 1970 set stringent 1975 model-year emission standards for light-duty passenger cars and authorized a one-year suspension if statutory conditions were met, including a showing that necessary technology was unavailable and consideration of a National Academy of Sciences (NAS) study.
- International Harvester and major automobile manufacturers applied to EPA for a one-year suspension of the 1975 hydrocarbon and carbon monoxide standards, submitting extensive prototype test data.
- The manufacturers’ evidence included testing on hundreds of prototype cars and catalytic converters; their results showed extremely limited compliance and no demonstrated durability over the required 50,000-mile period.
- NAS studies concluded the needed technology was not then available, warned of drivability and performance impacts, and indicated the ecological cost of a one-year extension would likely be small given existing 1974 standards.
- The EPA Administrator denied the suspension requests, adjusting or discounting aspects of the manufacturers’ test data (including assumptions about gasoline lead content and deterioration over time) and predicting that technology would be available in time for the 1975 model year.
- The petitions for review were consolidated in the U.S. Court of Appeals for the D.C. Circuit under the Clean Air Act’s judicial review provisions.

## Issues

1. Whether the EPA Administrator lawfully denied a one-year suspension by adequately explaining and supporting his prediction that compliant technology would be available for the 1975 model year.
2. How the evidentiary burdens operate where manufacturers present extensive noncompliance data and the agency responds with a predictive judgment about future technology.
3. Whether the Administrator adequately addressed significant contrary evidence, including the NAS conclusions and the manufacturers’ test results, so as to permit meaningful judicial review.

## Decision

- The D.C. Circuit did not order that a suspension be granted or denied on the merits.
- The court held the denial was not supported by an adequately explained, reasoned analysis of the reliability of the methodology used to predict technology availability.
- The court remanded to EPA for further proceedings and a more complete explanation sufficient to permit judicial review.

## Legal Principles

- Agencies may make predictive judgments about future technological capability when implementing statutory standards, but the prediction must be supported by a reasoned explanation grounded in evidence and disclosed methodology.
- When regulated parties make a substantial empirical showing supporting statutory relief, the agency must provide a reasoned response that explains why the evidence is rejected or outweighed and why the agency’s assumptions are reliable.
- Meaningful judicial review requires the agency to articulate a rational connection between the facts found (including treatment of key data adjustments) and the decision made, and to confront significant contrary evidence such as expert studies mandated by statute.
- Courts reviewing technical agency decisions do not substitute their own scientific judgment, but they may require the agency to supply a reviewable explanation and to correct analytical gaps through remand.

## Conclusion

The court required EPA to justify, with an adequately explained and reviewable methodology, its prediction that emissions-control technology would be available to meet the 1975 standards, and it remanded because the denial did not sufficiently explain critical assumptions or address contrary evidence such as the NAS findings and manufacturers’ test data.


International Harvester Co. v. Ruckelshaus, 478 F.2d 615 (D.C. Cir. 1973)