## 4 Experimental Environment for Truck Platooning
### Selection of Driving Simulator and Construction of Experimental Environment  
This study employed a high-performance driving simulator of the Korea Expressway Corporation (KEC) located at the Vehicle Driving Simulation Facility of the Road Traffic Research Institute. This simulator is utilized in various fields, including the new Electronic Toll Collection System (ETCS), traffic safety, Cooperative-Intelligent Transport Systems (C-ITS), and autonomous driving. It reproduces highly realistic driving experiences by enhancing vehicle dynamics during lane change and acceleration/deceleration through longitudinal and lateral rails and a six-degrees-of-freedom (DOF) actuator. The simulator consists of a real-time vehicle dynamics simulation module, three-dimensional (3D) video generation and display, audio generation and output, motion, capsule and control load systems, and integrated control and monitoring systems. This study constructed a virtual road traffic environment and implemented truck platooning on the driving simulator. The construction of the virtual environment involved two stages: (1) the creation of a high-definition (HD) map-based video database, and (2) the development of truck platooning strategies. For the driving simulator experiment, a realistic virtual environment based on a video database of the target road section is essential. In the HD map-based video-database construction stage, the video database was generated as 4D videos derived from HD maps, reflecting road surface conditions (e.g., slipperiness, slope, and curvature) and vehicle movement characteristics. The 3D-Max program was used to implement the geometry of the target section in the simulator. In the truck platooning strategy-development stage, realistic road environments and traffic conditions similar to actual platooning scenarios were reproduced. Because the objective of this study was to analyze drivers' psychological stability during platooning situations, the traffic environment was configured to reflect real-world conditions while minimizing the psychological instability caused by non-platooning-related traffic congestion. To this end, a level of service (LOS) B traffic environment (10 vehicles per km per lane) was applied. In all scenarios, the number of surrounding vehicles, driving speeds, and driving patterns were kept constant to exclude any psychological anxiety factors unrelated to the purpose of the experiment. Finally, the experimental vehicle automatically formed a platoon upon entering the test section and was set to drive in the outer lane, in compliance with the Road Traffic Act. Subsequently, truck platooning was implemented on the driving simulator. The simulator had an interchangeable cabin structure depending on the experimental conditions. The cabin is the space in which the participants ride and is driven by a motion platform, which simulates the form of a general vehicle. To replicate the actual truck driving conditions, a truck-shaped cabin was installed for the experiment. The motion platform was tuned, and the vehicle dynamics were adjusted to reproduce the detailed movements of the truck. In the final stage of constructing the experimental environment, the formation and dissolution characteristics of truck platooning were configured with reference to ISO/DIS 4272 and the KEC's research on \"V2X-based Truck Platooning Operation Technology Development\". The platoon formation and dissolution procedures from the perspective of the following vehicles are presented in Table 1, and the simulator and experimental environments used in the experiment are shown in Figure 1.