  Deep reinforcement learning (RL) has been shown to be effective in producing
approximate solutions to some vehicle routing problems (VRPs), especially when
using policies generated by encoder-decoder attention mechanisms. While these
techniques have been quite successful for relatively simple problem instances,
there are still under-researched and highly complex VRP variants for which no
effective RL method has been demonstrated. In this work we focus on one such
VRP variant, which contains multiple trucks and multi-leg routing requirements.
In these problems, demand is required to move along sequences of nodes, instead
of just from a start node to an end node. With the goal of making deep RL a
viable strategy for real-world industrial-scale supply chain logistics, we
develop new extensions to existing encoder-decoder attention models which allow
them to handle multiple trucks and multi-leg routing requirements. Our models
have the advantage that they can be trained for a small number of trucks and
nodes, and then embedded into a large supply chain to yield solutions for
larger numbers of trucks and nodes. We test our approach on a real supply chain
environment arising in the operations of Japanese automotive parts manufacturer
Aisin Corporation, and find that our algorithm outperforms Aisin's previous
best solution.
