  The rapid growth of pharmaceutical refrigerated logistics poses
sustainability challenges, including elevated costs, energy consumption, and
resource inefficiency. Collaborating multiple depots can enhance logistics
efficiency when standalone distribution centers have limited transport
resources, i.e., refrigerated vehicles. However, the sustainable benefits and
performance across different strategies remain unexplored. This study fills
this research gap by addressing a refrigerated pharmaceutical routing problem.
While many collaborative strategies prioritize economic and environmental
benefits, our approach highlights a vital social indicator: maintaining vehicle
flow equilibrium at each depot during collaboration. This ensures the stability
of transport resources for all stakeholders, promoting sustainable
collaborative logistics. The problem is formulated as a multi-depot vehicle
routing problem with time windows (MDVRPTW). Three collaborative strategies
using Clustering VRP (CLUVRP) and improved Open VRP (OVRP) are proposed and
compared. We develop two approaches to address traditional OVRP limitations in
ensuring vehicle flow equilibrium at each depot. Our models consider perishable
pharmaceuticals and time-dependent travel speeds. Three hybrid heuristics based
on Simulated Annealing and Variable Neighborhood Search (SAVNS) are proposed
and evaluated for efficacy. Computational experiments and a case study
demonstrate distinct sustainable benefits across various strategies, offering
valuable insights for decision-makers in the refrigerated logistics market.
