Traditional evaluations of public transportation systems have primarily focused on technical and economic efficiency, often overlooking broader societal and environmental contributions. Addressing these limitations, this study proposes a comprehensive evaluation framework that integrates operational performance, environmental impact, and social welfare dimensions. Building upon Fielding’s (1985) classical triangular model, we extend it into a triangular pyramid structure, enabling a more detailed decomposition of transportation efficiency into production, service, and value realization stages. Utilizing a three-stage Network Data Envelopment Analysis (NDEA) model, we systematically analyze the operational process of Keelung City's bus routes, capturing the efficiency of each sub-process through inputs, intermediate outputs, and final outputs. To enhance comprehensiveness, this framework incorporates CO₂ emissions as undesirable outputs in the service stage and societal welfare benefits in the value realization stage. This extension offers several conceptual and practical advantages. It enables a more flexible and detailed decomposition of Overall Efficiency, allowing it to be expressed not only as a weighted sum of Production Efficiency, Service Efficiency, and Generation Efficiency, but also through alternative decompositions: (i) as a weighted sum of Consumption Efficiency and Generation Efficiency, or (ii) as a weighted sum of Production Efficiency and Service-Generation Efficiency. The empirical analysis is expected to reveal significant efficiency disparities across bus routes. It is anticipated that high-efficiency routes will demonstrate a more balanced allocation of resources and outputs, while low-efficiency routes may exhibit severe resource wastage, elevated carbon emissions, and suboptimal operational performance. Routes with substantial inefficiencies are expected to be identified as candidates for targeted improvement strategies, such as schedule optimization, service frequency adjustments, and the deployment of environmentally friendly vehicles. This study contributes methodologically by advancing a multidimensional triangular pyramid framework for transportation performance evaluation and practically by providing actionable insights for optimizing public transit operations. The findings are expected to offer a valuable reference for policy formulation aimed at enhancing the economic, environmental, and social sustainability of urban bus systems, ultimately promoting effective resource allocation and maximizing societal welfare.

Network Data Envelopment Analysis (NDEA), Triangular Pyramid Framework, Bus Route Performance Evaluation, Societal Welfare Assessment, CO₂ Emissions