EXAMINING OPTIMAL TRUCK PLATOON CONFIGURATIONS TO MAXIMIZE ITS OPERATIONAL, SAFETY, AND ENVIRONMENTAL PERFORMANCE

Efficient movement of freight is a critical component of the US economy and especially important to the southcentral region where several large freight distribution hubs are located. However, several challenges affect freight movement efficiency, including high fuel and labor costs, vehicular emissions, and traffic safety problems. Truck platooning is a promising application of connected and automated vehicle (CAV) technology that has great potential in addressing current challenges in freight movement in the USA and elsewhere. Few prior studies have examined the potential environmental and traffic operational impacts of truck platooning on freeways. In particular, little is known regarding its impacts on traffic safety, especially at complex traffic areas of highways (e.g., merging and diverging segments). This study strives to examine and suggest the optimum configuration of truck platoons (size, spacing, penetration rate) that might maximize the positive operational, safety, and environmental impacts through an economic analysis. A section of Interstate 10 in Louisiana was selected as the study area that consists of several merging and diverging segments. The configuration of the platoons consist of platoon size (2,3,4, and 5 trucks) and intra-platoon distance which is the headway between the trucks (0.3, 0.5, and 0.7 seconds). The truck penetration rate, which is the percent of trucks that can form platoons, was chosen as 25% for the transition period, 50 % for the intermediate period, and 75% and 100% for the extreme periods. The operational, environmental, and safety impacts were assessed by Vissim, MOVES, and SSAM models, respectively. To quantify these impacts, network delay, fuel consumption, CO₂ emission, and the number of total conflicts (rear-end and lane change) were selected as the performance metrics. An economic analysis was conducted to convert the impacts of truck platoons in monetary values. Then the optimum truck platooning configurations were determined during peak and off-peak periods and at different truck penetration rates by comparing the overall cost. The findings revealed that truck platoons performed exceptionally well on the operational and environmental aspects. However, the traffic safety was substantially reduced with the presence of truck platoons, especially in the peak hour period. For the peak period, the optimum platoon size was found to be smaller with 3 trucks in the transition period (25% penteration rate), and 2 trucks for the intermediate to extreme periods (50% penteration rate or more). The optimum intra-platoon distance was found to be higher (0.7 seconds) for all truck penetration rates. For the off-peak period, smaller platoon size (3 trucks) with lower intra-platoon distance (0.3 seconds), or larger platoon size (4) with intermediate intra-platoon distance (0.5 seconds) can be used in the transition period (25% penteration rate) . When the truck penetration rate increases from transition to extreme periods, smaller platoon size with larger intra-platoon distance (2 or 3 trucks with 0.5 second for 50- 75% cases, and 2 trucks with 0.7 seconds for 100% case) is required to minimize the total cost of truck platooning. In almost all the cases, for a specific platoon size or intra-platoon distance, increasing truck penetration rate significantly reduced the total cost. The result indicates that the safety is a crucial parameter in determining the optimum truck platoon configuration. It is expected that the results of this research can help transportation authorities in improving operational, safety, and environmental benefits provided by truck platooning