Unraveling the relation between carbon emission and carbon footprint: A literature review and framework for sustainable transportation

Transportation decarbonization has drawn enormous attention globally, and two concepts play vital roles: transportation carbon emission (TCE) and transportation carbon footprint (TCF). However, their overlapping definitions and mixed uses in relevant literature have caused ambiguities and misunderstandings, resulting in a pressing need to clarify their subtle relationships in a more introspective manner. Therefore, we performed an in-depth literature review to investigate their essential commonalities and differences, with a focus on two aspects: understanding the scientific progress in terms of research trends, foci, and clusters to capture their connotations and use cases; and diagnosing how they are inherently estimated and how misuses can be alleviated. Accordingly, we developed an integrated life cycle analytical framework to relate TCE and TCF in an interdisciplinary landscape. Implications regarding systematic and explicit quantification standards were identified and discussed. Finally, we proposed three research gaps and four possible directions for future sustainable transportation studies.