This study uses empirical research of 145 projects on environmental impact assessment (EIA). The researchers generated and tested hypotheses based on questions about the effectiveness and quality of EIA. By means of EIA, aspects of proactive thinking have entered into procedural decisions more than previously presumed and modifications in the spatial dimensions of projects have played an especially prominent role. The three most important factors affecting the scale of general project modifications are: the degree to which the subject matter and methodological aspects of a study are prescribed by §5 of the EIA Act (Scoping); the early, intense involvement of authorities, experts, and third parties in the scoping; and the degree to which the project's effects and impacts are analyzed and forecast in the environmental impact study (EIS). EIA and EIS practice has moved beyond the ‘experimental phase’ and routines have now emerged for certain parts of the procedure.