## 5 Results and Discussion
### Spatial Interaction Between HDT Behaviors and Clustered Freight Zones
#### 5.4.6 Refrigerated Truck (RT)  
Figure 14 shows a systematic analysis of the trip patterns of RTs. As the core carriers in cold-chain logistics, refrigerated trucks exhibit a spatial distribution characterized by specialized hub agglomeration and regional distribution linkage, deeply reflecting the  
Figure 13: Systematic analysis of trip pattern of fence-sided trucks. The upper two subplots depict heatmaps of trip ends and trips, respectively. The Sankey diagram in the lower-left corner illustrates the proportions of FT trips across clustered functional zones, while the ID entropy heatmap in the lower-right corner visualizes entropy values in grid cells with high trip volumes.  
unique infrastructure dependencies of cold-chain transportation. The Sankey diagram analysis shows that Cluster 1 (28.17%) and Cluster 2 (50.94%) account for over 79% of RT trips, with 66% of intra-cluster movements within Cluster 1-2, confirming these zones' roles as cold-chain logistics trunk hubs and regional distribution centers. This pattern is directly linked to RTs' transportation of high-value goods (e.g., fresh produce and medical products), which rely heavily on air transport timeliness, bonded warehousing conditions, and large-scale cold-processing facilities.  
The spatial heatmap reveals that RTs densely cluster in nodes such as Pudong Air Cargo Zone, cold-chain logistics parks, and food processing bases, forming cold-chain corridors linking air hubs, cold storage clusters, and processing centers. Meanwhile, the low penetration in Cluster 4 (13.83%) indicates that heavy RTs primarily serve upstream and midstream cold-chain supply chain segments (e.g., factory-to-distribution center trunk transport), while last-mile delivery (e.g., fresh produce shelving in supermarkets) is predominantly handled by light-duty refrigerated vehicles.  
The concentration metrics (\(HHI_{E}\) = 0.36, \(HHI_{R}\) = 0.04) are both below medium levels. While the trip ends concentrate in specialized cold-chain facilities within Cluster 1 and 2, they do not result in monopolistic hub control; instead, they create multi-node agglomerations along the airport-cold storage-processing zone chain, reflecting cold-chain logistics' reliance on infrastructure networks. An ID entropy analysis further reveals organizational divergences. On one hand, the high ID entropy in wholesale markets, public cold storage, and logistics centers indicates diverse and flexible transport actors at these public service nodes. On the other hand, the low ID entropy in food processing and medical  
Figure 14: Systematic analysis of trip patterns of refrigerated trucks. The upper two subplots depict heatmaps of trip ends and trips, respectively. The Sankey diagram in the lower-left corner illustrates the proportions of RT trips across clustered functional zones, while the ID entropy heatmap in the lower-right corner visualizes entropy values in grid cells with high trip volumes.  
product factories reflects closed supply chain models dominated by in-house fleets or long-term contract carriers, such as the transport chain in between pastures, factories, and regional warehouses.