Koulaeian, M., H. Seidgar, M. Kiani, and H. Fazlollahtabar. “A Multi Depot Simultaneous Pickup and Delivery Problem With Balanced Allocation of Routes to Drivers”. International Journal of Industrial Engineering: Theory, Applications and Practice, vol. 22, no. 2, Oct. 2014, doi:10.23055/ijietap.2015.22.2.1379.