SUM, S., S. Jomnonkwao, T. Champahom, R. Beeharry, and V. Ratanavaraha. “Measuring the city bus service quality based on users’ perceptions: City bus service in Phnom Penh, Cambodia”. Engineering and Applied Science Research, vol. 47, no. 1, Mar. 2020, pp. 47-55, https://ph01.tci-thaijo.org/index.php/easr/article/view/202981.