Vehicles equipped with adaptive cruise control (ACC) systems are expected to improve traffic safety and decrease fuel consumption. Recent studies have shown that ACC leads to string instability in the case of platooning and can therefore result in higher energy needs compared to a platoon of human-driven vehicles (HDV). However, the impact of the ACC on fuel consumption in the case of platooning and the global impact of ACC overconsumption in traffic is not known yet. This study examines the impact of ACC systems on traffic consumption using experimental data and traffic records. In this study, we inject the speed profiles of ACC and HDV platoons that follow a similar leader trajectory into an engine bench. Then we identify the event that leads to an overconsumption in the case of platooning. Using HighD and ExiD records, we detect if the events leading to overconsumption often happen in traffic. The results of the engine bench show that only ACC platoons of six or more vehicles with a short time-gap setting consume more than HDV platoons. The results on HighD and ExiD show that such an event happens£ once out of 1250 if we divide the time into steps of 15 seconds. This shows that even if overconsumption exists in specific cases, it is too rare in traffic to impact global fuel consumption.