Passenger satisfaction with metro bus services is critical for sustainable urban mobility but remains underexplored in Pakistan. Using Partial Least Squares Structural Equation Modeling (PLS-SEM) on survey data from 400 households in Islamabad, this study identifies the main service-quality drivers of satisfaction. Safety and assurance, reliability, responsiveness, and automated systems emerge as the strongest predictors, while demographic factors and distance to stops show little influence. These findings suggest that prioritizing safety, reliability, and technology-based improvements could enhance passenger experience and inform policies aligned with SDG 9 (Industry, Innovation, and Infrastructure) and SDG 11 (Sustainable Cities and Communities).