Transportation systems play a vital role in sustainable development and have a profound impact on social, environmental, and economic sustainability in urban environments. Integrating decision support systems is essential to emphasize the need for change and facilitate policy decisions based on current conditions. This study evaluates the urban public transportation system of Tehran, Iran, with the aim of promoting sustainability. In this research, transportation experts in Tehran were used as evaluators. This study uses the Size-Based Fuzzy Analytic Hierarchy Process (MFAHP), which was selected for its accuracy and computational efficiency compared to existing methods. The results obtained are consistent with those of the modified fuzzy logarithmic least squares method, confirming its validity. Comparative and sensitivity analyses validate and test the findings of the proposed model for stability and robustness. The study concludes that the introduction of new buses is recognized as the most effective solution to improve the quality of service of the existing transport system. The results obtained from a real dataset and its application in the assessment of transport and the recommendation of new buses as the optimal solution provide insights into the development of sustainable urban transport.