The following questions were addressed in this study: How can environmental impacts of transport be identified? How can the impacts be represented by operational indicators? How can several indicators be considered jointly? How can indicators be used in planning and decision making? First, a definition of the phrase “indicator of environmental impacts in the transport sector” was derived. The concept of a chain of causality between a source and a final target was developed as a common reference for indicators and their assessment. Criteria and methods for the assessment and selection of indicators were derived in terms of measurement, monitoring, and management. Finally, examples of the application of the criteria for individual indicators of seven chains of causality and for selected aggregated indicators were developed and are presented in this paper.