# Efficient Position Change Algorithms for Prolonging Driving Range of a Truck Platoon
## 2 Literature Review
The experiments were carried out with a steady-state speed from 55 mph to 70 mph or approximately 88 km/h to 113 km/h, with inter-vehicle gaps ranging from 20 ft to 75 ft or about 6 m to 23 m, and the total gross vehicle weights (GVW) of 65,000 lbs and 80,000 lbs. According to the experimental results, significant fuel savings can be achieved for both leading and trailing trucks where the first truck experienced up to 5.3% of fuel-saving, and the second truck experienced up to 9.7% fuel-saving. The best configuration is 88 km/h constant velocity, roughly 9 m inter-vehicle distances, and 65,000 GVW, which results in 6.4% fuel consumption reduction in the whole convoy. They further conclude that atmospheric conditions and heavy loads of trucks may significantly influence in savings attainable, considering heavily loaded vehicles consume fuel at a higher rate because of the increased airflow. Truck platooning system experiments and studies have been summarized through [PERSON] et al. 's work ([PERSON] et al., 2020) in 2020. The longitudinal space is considered the highest influencing factor in truck platooning fuel economy. The position and vehicle configurations are also made to the top-tree highest respectively. In summary, the overall performance of fuel consumption reduction in a platoon can be increased with closer longitudinal space. The vehicle's position in the platoon influences fuel consumption in the way that trailing vehicles always experience more fuel savings and even more in next-order trucks due to the less aerodynamic drag. Masses and loads also significantly affect the percentage of fuel savings in the platoon, as the heavy loads consume fuel much more than the ordinarily loaded or empty trailer trucks. All of the previous studies that we have discussed so far come to the conclusion that influencing factors such as longitudinal spacing, a vehicle position in a platoon, and vehicle configurations, affect the effectiveness of energy-saving in the truck platooning system. These factors influence the reduction of aerodynamic drags, thereby achieving reduced fuel consumption consistently. Nevertheless, experimental tests conducted under different conditions can cause different results, where the optimal solution for truck configurations cannot be determined. This is because it depends on various uncontrollable conditions, including road grades, presences of traffic, and weather conditions, which are restricted in reality. Still, these studies help us understand the influence of positions in a platoon on the unequal distributions of fuel consumption reduction, thus urging us to address the remaining challenge to improve fuel efficiency optimally. In our previous work ([PERSON] et al., 2020), we have introduced the position change problem, of which the objective is to prolong the driving range with the given amount of initial fuel. We have also proposed two heuristics (\"Fuel Amount Heuristic (FAH)\" and \"Traveling Time Heuristic (TTH)\") for the position change problem to enable the platoon to drive as far as possible and reach the maximum driving range or distance, thus enhancing fuel-saving the most. The difference between the two heuristics is the conditions when the vehicles should change their positions. In \"Fuel Amount Heuristic\", the platoon starts in the order of the initial fuel amount of the trucks. For any two adjacent vehicles, if the remaining fuel of the leading truck is less than the remaining fuel of the trailing truck by more than a threshold \(c\), then the two vehicles should change their position. The intuition is that we want to put a vehicle with more energy into the front positions, but not so frequently. In the \"Traveling Time Heuristic\" algorithm, we first divide the time into multiple time slots. At the beginning of each time slot, the truck with the highest fuel moves to the front of the platoon and the second-highest moves to the second position, and so forth.