Students, industry, and departments of civil engineering are engaging interdisciplinary learning techniques to promote sustainability and meet the urgent requirements of human development. However, only a few pieces of literature discussed the learning efficiency and educational feedback of this trend. This may be resulted from the difficulty in estimating subjective engagement. Hence, this study surveyed 173 data from 6 departments that provided interdisciplinary courses based on three dimensional trapezoidal fuzzy numbers and Likert scale. The questionnaire factors were modified from the useful and common scales in Science, Technology, Engineering, and Mathematics (STEM) education. Existing studies tend to estimate students' learning efficiency based on the hybrid approach of Data Envelopment Analysis (DEA) and Principal Component Analysis (PCA) methods. However, the meaning of variables may be changed in the PCA's procedures of axis transformation. Hence, a new fuzzy DEA-Mahalanobis distance approach was proposed to solve this problem. Based on the student gains in the sustainability courses, three groups were clustered and compared. Feedback for students was suggested to improve learning strategies. The sensitivity analysis showed that ''effective teaching practice'' and ''learning from other open courses or YouTube'' are key factors in increasing learning efficiency in the sustainability courses for civil engineering students. Therefore, this paper provided a useful and easy approach to improve learning strategies for civil engineering students in sustainability education.