“…Since the 1990s, most research has focused on the VSP with multiple depots (MDVSP) (Kliewer et al, 2006), which is proven to be NP-hard by Bertossi et al (1987). Meanwhile, more realistic characteristics have been included, such as fuel consumption (Haghani and Banihashemi, 2002;Li, 2014), time windows (Desaulniers et al, 1998;Kliewer et al, 2011), multiple vehicle types (Kliewer et al, 2006;Ceder, 2011;Hassold and Ceder, 2014), integration with timetabling (Ibarra-Rojas et al, 2014), integration with crew scheduling (Huisman et al, 2005;Shen and Ni, 2006;Shen and Xia, 2009;Shen and Zhao, 2009;Steinzen et al, 2010), and integration with crew scheduling and rostering (Mesquita et al, 2013).…”