# Steady-Speed Traffic Capacity Analysis for Autonomous and Human-Driven Vehicles
## 4 Results
### Average Clearance Analysis  
The RPLIDAR device used in the field experiment directly recorded the clearances between every two following vehicles. Figures 5-7 illustrate the clearances for all types of vehicles during driving at low constant speeds of 30, 40, and 50 km/h. The distribution of clearances for each vehicle category is interpreted using a Lollipop diagram. In this diagram, dots represent the mean clearances for the corresponding driving category, and each dot is connected by a vertical line, representing the average clearances for the entire dataset. From the above illustrative figures, it is evident that clearances obtained by human-driven vehicles (red) are shorter than those of all other ACC-equipped vehicles at this low range of constant speeds. The average clearances for human-driven vehicles were only 7514, 9846, and 12,420 mm, respectively. Vehicles equipped with Volvo's combined camera and radar ACC sensor recorded the closest average clearance, measuring 7985 mm at 30 km/h. As the driving speed increased, Subaru achieved the second-shortest average clearance, measuring 10,537 mm at 40 km/h and 11,732 mm at 50 km/h, utilizing Eyesight technology. Conversely, VW demonstrated safer following distances using radar ACC during this phase of the experiment, with all individual average values falling below the overall average line. Figure 5: Vehicle clearances at driving speed of 30 km/h. Figure 6: Vehicle clearances at driving speed of 40 km/h. In the next phase of the experiment, the vehicles' performance was tested at medium constant driving speeds of 60, 70, and 80 km/h. The results showed a consistent pattern of shorter clearances, with the following order for the mentioned speeds: Human-driven, Subaru, Volvo, and then VW. The minimum differences in average clearance between the human-driven and the nearest ACC vehicle for the three speeds were 451, 1456, and 587 mm, respectively. Meanwhile, the maximum differences between the human-driven and the farthest vehicle were recorded as 3567, 3200, and 3588 mm, respectively. Figures 8-10 illustrate the performance of vehicles to provide the shortest clearances during driving at medium speeds. Later, at high-speed ranges of 90, 100, and 110 km/h, human-driven vehicles continued to follow the leading vehicle at closer distances. In contrast, ACC vehicles exhibited varying following behavior. For example, at 90 km/h, Volvo was the second vehicle to generate the shortest distances ahead, while at 100 and 110 km/h, it provided the largest average clearance among the vehicles. Subaru, on the other hand, closely mirrored human-driven behavior at the maximum test driving speed of 110 km/h, with recorded average clearances of 27,247 mm for Subaru and 27,211 mm for the human-driven vehicle. The oscillation behavior exhibited by ACC vehicles at high speeds may become a limitation to their performance. Figures 11-13 depict the distribution of the clearances at the high range of driving speeds. Figure 8: Vehicle clearances at driving speed of 60 km/h. Figure 7: Vehicle clearances at driving speed of 50 km/h. Figure 11: Vehicle clearances at driving speed of 90 km/h. Figure 10: Vehicle clearances at driving speed of 80 km/h. Figure 9: Vehicle clearances at driving speed of 70 km/h. Overall, the result emphasized the fact that humans tend to exhibit a more assertive driving style compared to the utilization of ADAS represented by driving using ACC tools. This characteristic is particularly evident in their ability to make dynamic decisions regarding the proximity to other vehicles based on the intricacies of the driving environment and spatial configurations. The discretionary nature of human decision making during the driving task emerges as a distinctive advantage, allowing for nuanced adjustments in following distances. An additional noteworthy observation pertains to the discernible dissimilarity in the distribution of data around the means for vehicles operated by humans across all tested speeds.