AbstractFlexible pavements are prone to premature deterioration, and researchers are unresolved regarding the importance of the underlying causes resulting in inappropriately selected modeling parameters and increased uncertainty in predicting subsequent behavior and performance. A windshield survey, literature survey, and fuzzy Delphi study were undertaken as complementary approaches to costly conventional investigations to identify reasons for flexible pavement deterioration in the design, construction, and life span phases. Overall, the results revealed that the life span phase consists of the most contributors to pavement deterioration, which is approximately twice as much as the design and construction phases. However, the findings suggest that most causes of deterioration in the life span phase can be attributed to deficiencies in the preceding phases. Experts believe that structural and traffic are the most significant contributors to pavement deterioration, more so than construction, environment, and maintenance factors. Additionally, the surface and subgrade layers were deemed to be the most problematic. Applying the fuzzy Delphi method minimizes the ambiguities associated with the causes of pavement deterioration identified in the literature and is advantageous for limited data. This study proposes measures for improving the design and construction of more sustainable tropical pavements. Improved knowledge of the causes of deterioration is vital for selecting the appropriate design, construction, and maintenance strategies.