# Improving Freight Traffic Efficiency at Urban Intersections Using Heavy Vehicle Platooning
## 3 Methodology
### Advisory Speed Trajectory Algorithm  
The advisory speed trajectory algorithm employs different strategies to optimize traffic flow and safety, aiming to minimize the number of stops and reduce travel time by allowing some heavy vehicles (HCVs) to accelerate and pass through intersections before the traffic light turns red. This approach ensures smoother traffic flow by enabling some HCVs to clear the intersection without stopping. To achieve this, the algorithm modifies the Intelligent Driver Model (IDM) to better accommodate the unique operational constraints of heavy vehicle drivers approaching the intersection. The algorithm continuously searches for the optimal platoon departure order using Equation (4) at each time step, prioritizing the departure sequence that minimizes the average vehicle delay. An advisory speed is assigned to the lead HCV of each platoon based on three distinct scenarios:  
1. **Maximum Speed Strategy**: If the platoon can reach the intersection within the current green phase while maintaining the flow speed, it follows the maximum speed strategy. The advisory speed is set to the predefined maximum allowable speed (\(V_{max}\)), which aligns with legal speed limits for heavy vehicles.
2. **Deceleration Speed Strategy**: If the platoon cannot reach the intersection within the current green even at \(V_{max}\), but can reach the next green phase while traveling within the allowable speed range (\(V_{min}\leq V\leq V_{max}\)), it follows a deceleration speed strategy. The advisory speed is adjusted dynamically to ensure smooth progression without stopping.
3. **Deceleration Stop Strategy**: If the platoon cannot reach the current green at \(V_{max}\) and would arrive too early at the next green phase even at \(V_{min}\), the deceleration stop strategy is applied. In this case, the platoon follows a gradual deceleration while  
Figure 5: Flowchart of the optimum departure sequence identification.  
maintaining a safe driving speed until it reaches the intersection. The deceleration rate follows the standard behavior modeled in VISSIM's internal engine for heavy vehicles.  
To ensure the algorithm's effectiveness, the advisory speed updates are synchronized with the simulation time step, allowing real-time adjustments based on traffic conditions. The threshold for selecting the maximum speed strategy is determined by a predefined time-to-intersection value relative to the green light duration. This ensures that platoons are dynamically assigned speeds that optimize their progression while avoiding unnecessary stops. Additionally, if a platoon cannot pass within the available green time due to signal constraints, the algorithm dynamically shifts its strategy by either adjusting speed or transitioning it to the next green cycle.  
By integrating the Intelligent Driver Model (IDM) with the three adaptive speed scenarios, the proposed advisory speed trajectory algorithm effectively reduces the number of stops, minimizes delays, and enhances intersection efficiency for heavy vehicle platoons. Figure 6 visually demonstrates the impact of this approach on HCV progression through intersections.