An integrated novel interval type-2 fuzzy MCDM method to improve customer satisfaction in public transportation for Istanbul

•The criteria improve customer satisfaction in public transportation are determined.•The questionnaire used in this study is applied at bus stops and Metrobus stations.•An integrated novel interval type-2 fuzzy TOPSIS and GRA method is proposed.•A numerical application is presented in public transportation companies in Istanbul.•The method can be applied to complex decision making problems encounter vagueness. In this paper, the problems of public transportation customers in Istanbul are addressed and their satisfaction levels are evaluated by using customer satisfaction survey and statistical analysis. A novel interval type-2 fuzzy MCDM method is proposed based on TOPSIS and GRA, to evaluate and improve customer satisfaction in Istanbul public transportation. Then, the criteria need to be improved are determined and different improvement suggestions are made for all public transportation firms.