Environmental lawsuits against federally aided highway projects, like other attempts to litigate the environmental effects of governmental projects that have been in formulation for many years, often face the argument that recently enacted laws designed to protect the environment do not apply to projects that were already in progress, but still incomplete, when the laws were passed. Generally the impact of the new statute on ongoing projects is probed by asking two questions: How far advanced was the project on the date when the statute or regulation became effective? Did Congress or the agency intend to impose the new environmental constraints on projects that had already proceeded this far? Answers to these questions must be premised on a detailed analysis of the relevant agency's decisionmaking process, an assessment of decisions remaining to be made, a construction of the environmental statute or regulation, and, if the intent of Congress or the agency is not plain, a review of the provision's legislative or administrative history.

Determining the stage of development of a governmental project is problematic, because formal decisionmaking processes defined by statute and regulation and the informal working relationships and patterns of decision that grow up around the formal process frequently conflict in practice. Difficult and complex federal administrative decisionmaking is usually fragmented, with initial responsibility for separate components dispersed among several administrators. When some part of the decisionmaking process has been completed, quite naturally there arises a partial, informal commitment to a final result that will not require rethinking initial parts of the process. Thus, a sense of finality may be developed before the formal decision, as defined by statute and regulation, has been made.