Optimization of Truck Platoon Size in Freeway Diverging Areas Based on Comprehensive Performance Evaluation

Truck platoons can enhance traffic throughput, achieve better fuel economy, and yield environmental benefits. However, in freeway diverging areas, excessively long truck platoons can cause a blocking effect on small vehicles exiting the freeway, thereby causing congestion and impacting the traffic flow in the section. Therefore, to balance the benefits between truck platoons and small vehicles, a comprehensive evaluation model was established, considering traffic efficiency, safety, and fuel economy. The analytic hierarchy process (AHP) method was employed to determine the importance of each indicator, resulting in a composite score. Using the Simulation of Urban Mobility (SUMO) platform, this paper examines the effects of truck platoon size (ranging from 2 to 15 trucks) on traffic efficiency, safety, and fuel consumption under varying conditions. The analysis considers low, medium, and high small vehicle traffic volumes of 750, 1200, and 1650 pcu/h/lane, as well as off-ramp probabilities for small vehicles of 10%, 20%, 30%, and 40%. Simulation results indicate that traffic efficiency initially increases and then decreases as the truck platoon size increases. An increase in the number of truck platoon members leads to a decrease in section safety, particularly noticeable under medium and high flow conditions. In three flow scenarios, truck platoon size of more than 5 trucks can achieve higher fuel economy. Taking an off-ramp probability of 10% for small vehicles as an example, the optimal truck platoon size ranges from 3 to 8 vehicles under low flow conditions, 2 to 7 vehicles under medium flow conditions, and 2 to 6 vehicles under high flow conditions. Hence, traffic managers in freeway diverging areas can utilize the findings of this study to select suitable truck-platoon size, enabling them to implement preemptive adjustment strategies for achieving optimal comprehensive performance.