  The Dynamic Pickup and Delivery Problem (DPDP) is aimed at dynamically
scheduling vehicles among multiple sites in order to minimize the cost when
delivery orders are not known a priori. Although DPDP plays an important role
in modern logistics and supply chain management, state-of-the-art DPDP
algorithms are still limited on their solution quality and efficiency. In
practice, they fail to provide a scalable solution as the numbers of vehicles
and sites become large. In this paper, we propose a data-driven approach,
Spatial-Temporal Aided Double Deep Graph Network (ST-DDGN), to solve
industry-scale DPDP. In our method, the delivery demands are first forecast
using spatial-temporal prediction method, which guides the neural network to
perceive spatial-temporal distribution of delivery demand when dispatching
vehicles. Besides, the relationships of individuals such as vehicles are
modelled by establishing a graph-based value function. ST-DDGN incorporates
attention-based graph embedding with Double DQN (DDQN). As such, it can make
the inference across vehicles more efficiently compared with traditional
methods. Our method is entirely data driven and thus adaptive, i.e., the
relational representation of adjacent vehicles can be learned and corrected by
ST-DDGN from data periodically. We have conducted extensive experiments over
real-world data to evaluate our solution. The results show that ST-DDGN reduces
11.27% number of the used vehicles and decreases 13.12% total transportation
cost on average over the strong baselines, including the heuristic algorithm
deployed in our UAT (User Acceptance Test) environment and a variety of vanilla
DRL methods. We are due to fully deploy our solution into our online logistics
system and it is estimated that millions of USD logistics cost can be saved per
year.
