Although customer satisfaction surveys are widely utilized by transit agencies, there are limited analyses in the literature on the perception of passengers as a result of service improvements. A before-after study can help to evaluate the effect of changes from customers points of view and thus guarantee a continuous improvement in the service. In this paper, customer satisfaction was directly observed through a Customer Satisfaction Survey (CSS) before and after certain changes. Furthermore, Structural Equation Modeling (SEM) is utilized to evaluate pas-sengers perception of the service attribute importance. Finally, an Importance-Performance Analysis (IPA) is adapted to analyze the changes in satisfaction and importance from the passengers perspective on each service attribute. In both before and after cases, a consistent SEM structure is used. The follow-up IPA provides transit agencies with priorities to improve service attributes and helps managers to devote their resources to key attrib-utes that matter to the riders. Metro line 3 in Tehran was selected as the case study which is 33.7 km long with 25 stations. Two surveys were performed one before (with the sample size of 300), and one after (with the sample size of 384) a set of changes the most important of which was a headway reduction. The SEM was developed with five latent variables of main service, comfort, information, protection, and physical appearance. This structure was assessed on both the before and after data collections and showed to be valid. Security at the station and security on board were the most important service attributes in both waves according to their factor loadings, while ethics and behavioral messages had the smallest factor loading and the least importance. Comparing the attributes in both surveys suggested that reducing the headway was effective, although it did not seem to be sufficient for en-hancing the overall customer satisfaction and improvements need to be continued.

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