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This paper tests whether impact analysis pursuant to the National Environmental Policy Act delays federal decision making, and whether the NEPA process results in significant changes to the substance of federal decisions. We reviewed 636 rules designating critical habitat for species that are protected by the Endangered Species Act. Because of a circuit court split, some of these rules were subject to NEPA analysis while others were not. In comparing these two groups we found that rules that underwent NEPA analysis were completed more than three months faster than rules that were exempted from NEPA review. We also found that rules that were subject to NEPA review underwent less change in the size of the habitat area between the proposed and final rule than those that were exempted from NEPA.