  This paper studies the optimal hub-based platoon formation at hubs along a
highway under decentralized, distributed, and centralized policies. Hubs are
locations along highways where trucks can wait for other trucks to form
platoons. A coordinator at each hub decides the departure time of trucks, and
the released trucks from the hub will form platoons. The problem is cast as an
optimization problem where the objective is to maximize the platooning reward.
We first show that the optimal release policy in the decentralized case, where
the hubs do not exchange information, is to release all trucks at the hub when
the number of trucks exceeds a threshold computed by dynamic programming. We
develop efficient approximate release policies for the dependent arrival case
using this result. To study the value of information exchange among hubs on
platoon formation, we next study the distributed and centralized platoon
formation policies which require information exchange among hubs. To this end,
we develop receding horizon solutions for the distributed and centralized
platoon formation at hubs using the dynamic programming technique. Finally, we
perform a simulation study over three hubs in northern Sweden. The profits of
the decentralized policies are shown to be approximately 3.5% lower than the
distributed policy and 8% lower than the centralized release policy. This
observation suggests that decentralized policies are prominent solutions for
hub-based platooning as they do not require information exchange among hubs and
can achieve a similar performance compared with distributed and centralized
policies.
