This research was conducted with the aim of identifying and prioritizing the factors affecting urban traffic congestion and inefficiency in Behbahan city. In the first stage, using the Delphi method and consensus of experts in the fields of urban management, transportation, urban development, and traffic police, a set of initial factors was extracted. Then, the data collected in the form of a fuzzy questionnaire with a Likert scale were analyzed using the fuzzy TOPSIS multi-criteria decision-making method. The reliability of the instrument was examined by calculating the Cronbach's alpha coefficient, the total value of which was equal to 0.951, indicating a very favorable internal consistency of the questionnaire. The results of the analysis showed that the "land use and urban structure" index, by obtaining the first rank, has the greatest impact on the urban traffic situation. After that, the "Economic factors," "Geometry," "Urban landscape," "Social and cultural factors," and "Traffic management" indices were ranked next, respectively. At the item level, factors such as “narrow street width,” “concentration of active commercial units along main streets,” “inadequate urban traffic management,” “presence of physicians’ offices,” “increase in private vehicles,” and “non-compliance with traffic laws and culture” were identified as the most important factors affecting urban traffic congestion. These results can be used as the basis for formulating corrective strategies in the field of urban planning, road design, and public transportation policymaking in medium-sized cities of Iran.