Emerging optimization problems for distribution in same-day delivery

Same-day delivery (SDD) has become a new standard to satisfy the "instant gratification" of online customers. Despite existing powerful technologies deployed in last-mile delivery, SDD services face new decision-making challenges on the tradeoff between delivery costs and time. In addition, new concerns on environmental issues, customer satisfaction, and fairness arise. Researchers have explored various approaches to face these challenges in SDD, where data uncertainty plays a fundamental role. In this paper, we carefully review the emerging routing problems and solutions proposed in the existing literature for SDD services. We survey papers on how to manage dynamic order arrivals, how to allocate time slots for deliveries, how to select the right delivery options, how to design pickup and delivery routes, and how to partition delivery areas and decide the composition of the fleet. We also propose mathematical formulations for representative problems. Finally, we sketch managerial insights and identify future research directions.