1. Avella J.R.: Delphi panels: research design, procedures, advantages, and challenges. IJDS 11(1), 305–321 (2016)
2. Aziz A., Mohamad J.: Urban public transport in Penang: Some policy considerations. EASTS 9, 1–19 (2013)
3. Basyir M.: Penang Ferry malfunctions for the second time this month. https://www.nst.com.my/news/nation/2018/07/393877/penang-ferrymalfunctions-second-time-month (2018). Accessed 1 Dec 2019
4. Bernama: Penang ferry service worsening. http://english.astroawani.com/malaysianews/penang-ferry-service-worsening-117821 (2016). Accessed 15 Dec 2019
5. Rowe G., Wright G.: The Delphi technique as a forecasting tool: issues and analysis. IJF, 15(4), 353–375 (1999)