@article{cattaruzza2016vehicle,
  title={Vehicle routing problems with multiple trips},
  author={Cattaruzza, Diego and Absi, Nabil and Feillet, Dominique},
  journal={4OR},
  volume={14},
  number={3},
  pages={223--259},
  year={2016},
  publisher={Springer Berlin Heidelberg},
  doi = {http://dx.doi.org/10.1007/s10288-016-0306-2}  
}