## 5 Results and Discussion
### Spatial Interaction Between HDT Behaviors and Clustered Freight Zones
#### 5.4.3 Specialized Truck (ST)  
Figure 11 shows a systematic analysis of the trip patterns of specialized trucks. Specialized trucks, including concrete mixers, oil tankers, and chemical tankers, serve as dedicated vehicles for industrial raw material and special cargo transportation, exhibiting a spatial pattern characterized by industrial-node agglomeration and peripheral radiation services.  
The Sankey diagram analysis reveals Cluster 1 (27.56%) and Cluster 2 (41.5%) account for over 69% of ST trips, as these zones house cement plants, chemical facilities, and large industrial logistics nodes, key hubs for special cargo production and transshipment. Plus, by overlay OpenStreetMap (OSM) waterway data, it is revealed that the trip hotspots of ST closely coincide with cement factories along inland riverbanks. This spatial pattern is driven by both the significant reduction in raw material logistics costs through waterway transportation and the critical dependence of cement production on abundant water resources. Operating with these industrial sites as focal points, specialized trucks employ a hub-and-spoke model of short-haul, high-frequency transport to serve peripheral demand points like construction sites, forming localized production-to-usage closed loops. This pattern directly reflects the cargo-specific constraints requiring short distances and time sensitivity, such as the limited initial setting time of concrete or safety protocols for hazardous chemicals. Additionally, the high-frequency trips at these industrial nodes and the specialized nature of specialized truck fleets contribute to their classification into Clusters 1 and 2, with clustering outcomes varying by trip volume intensity.  
Figure 11: Systematic analysis of trips pattern of specialized trucks. The upper two subplots depict heatmaps of trip ends and trips (with clustered labels), respectively. The Sankey diagram in the lower-left corner illustrates the proportions of ST 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.  
In terms of concentration metrics, specialized trucks exhibit an \(HHI_{E}\) of 0.284 (the second lowest value) and an \(HHI_{R}\) below 0.01 (the lowest value). These values highlight that while trips are concentrated at industrial core nodes, their single-center, multi-periphery divergent structure arises from serving dispersed peripheral demand points. Their penetration into Cluster 4 (15.25%) and Cluster 6 (10.81%) further demonstrates their role in non-core industrial scenarios, primarily related to construction activities. The ID entropy analysis shows low entropy in high-ST-trip zones, reflecting the sector's stringent qualification requirements, strict safety regulations, and stable organizational models. This specialization underscores how ST operations are shaped by both the technical limitations of cargo types and the regulatory frameworks governing industrial logistics, reinforcing the critical role of functional clustering in explaining vehicle-specific travel dynamics.