Phannikul, T., and S. Sindhuchao. “A Customized Tabu Search for the Vehicle Routing Problem With Simultaneous Pick-up and Delivery”. Science & Technology Asia, vol. 15, no. 2, Oct. 2015, pp. 70-82, https://ph02.tci-thaijo.org/index.php/SciTechAsia/article/view/41295.