## 2 Autonomous Vehicle Take over Simulation  
### Human-in-the-Loop Vehicle Simulator  
Using a driving simulator for control transfer or HMI design has the following advantages: Various event scenarios can be created, and they can be provided equally to several experimenters. Experiments can be carried out even in high-risk situations where accidents may occur. For these reasons, related studies mainly used driving simulators [30; 31; 32; 33; 34]. To provide real vehicle experiences in the driving simulator, visual, auditory, and tactile cues and a vehicle motion generation system are important [35]. The driving simulator can be  
Figure 2: Takeover process [17].  
effectively used to study abnormal driver patterns such as drowsiness, fatigue, drunkenness, and taking drugs [36; 37]. The experiment's validity using the driving simulator was verified by comparing the driver's responsiveness in the simulator and the real-world vehicle in several studies [38; 39; 40; 41; 42]. In a paper comparing the results of fixed-driving simulations with field tests, the validity of the simulation was verified in terms of surrogate task performance, visual attention, and driving performance [38]. The feasibility of driving simulators for speed, car-following distance, and reaction latency in the work zone was revealed, and some driving behaviors were slightly more aggressive in the simulator [39]. It was suggested that low-cost or fixed-base simulators could achieve similar effects to high-cost simulators and that the most important element for a successful behavioral validation study is a carefully designed experimental procedure and correct interpretation of the results [40]. It was found that there was no statistically significant difference between the simulator and the on-road vehicle for the human factor associated with the automated vehicle [41].  
Figure 3 indicates the HITL simulator used in this study and depicts of the parts interacting with the driver and the actual hardware. The driver's steering, gear, and pedal inputs were collected from a laptop and real-time processor and were transmitted to the main PC where the simulator was driven. The virtual driving environment was presented to the driver, visually very similar to what is seen from the driver's seat of an actual vehicle, through a large-screen (55 inches) 4 K resolution TV. A touch monitor for NDRT was placed between the driver and the TV. Static environments such as roads, traffic lights, and buildings, as well as dynamic obstacles such as vehicles, pedestrians, and bicycle occupants, were implemented using IPG CarMaker. This software provides solutions for virtual test driving, including basic vehicle systems such as dynamics and powertrain, driving scenario generators, autonomous driving sensor models, and realistic visual graphics.  
In the driving simulator, the steering torque feedback and pedal haptic feedback considerably influenced the driving accuracy, environmental awareness, and realism [43; 44]. The overall configuration of the steering system and controller is illustrated in Figure 4. A steering system that can output a maximum torque of 17 Nm was designed to implement real vehicle torque feedback by connecting a reduction gearbox to a smart motor with a nominal power of 615 W. An encoder and a torque sensor mounted on the shaft were used to measure the steering input of the driver.  
Figure 3: HITL simulator.  
In autonomous driving, the control algorithm manipulated the steering hardware, and the steering angle (as measured by the encoder) was input into the simulation. In manual driving, the steering was controlled by a torque control mode consisting of a road reaction torque calculated in the vehicle dynamics simulator (CarMaker) and an assist torque that reduced the steering load. The latter was inversely proportional to the driving speed, which provided comfortable steering at low speeds and stable control at high speeds.