## 3 Results
### Driving Performance Test
#### 3.1.2 Experimental Conditions  
First, the previous scenario conditions were replicated in the testing platform. Second, the NMPC controller of Section 2.1 was used to reproduce the driving modes. Finally, the experimental procedure consisted of five drivers running the tests, using four different driving modes, under two cognitive conditions (concentrated and distracted). The driving simulator shown in Figure 7 held the driving tests. The key component is the steering wheel interface, composed of a motor model 130 ST with a maximum nominal torque of 15 Nm, with configurable damping and inertia via software (this allows a practical integration of the stability criterion \(b_{\lambda}\)). It is also equipped with an incremental encoder and a current sensor that is used to calculate the applied torque. Behind the steering wheel, there is a Basler ACE acA1920--40 uc camera with a Sony IMX249 CMOS sensor, which performs the driver monitoring task. A Linux PC is used to perform the image processing through a convolutional neural network model to detect the driver's head position [43]. The automated driving software is an in-house vehicle dynamic simulation tool c (_Dynacar_[44]) which considers a vehicle's physical model based on multibody formulation. The control and decision algorithms are developed in MATLAB/Simulink, while the NMPC solver is the ACADO Toolkit [45], capable of obtaining optimal solutions in microseconds. The front screens allow the driver to see the driving environment, while the second task is held in a touch monitor using the right hand. The driving modes are used to compare different types of assistance when the driver is performing a secondary task. MANUAL mode is used as a baseline, and it represents \"no assistance\". Moreover, two commercial ADAS are included: lane keeping assist (LKA, used within this paper as LK) and automated lane centering (ALC, referred to in this work as LC). As the use of these terms by OEMs tends to be misleading, we are using the definition of the National Highway Traffic Safety Administration (NHTSA) [46]. LK actively keeps the vehicle within the lane by intervening as the vehicle approaches the lane boundaries. However, there is a dead band near the center of the lane where the LK system does not provide control. LC, instead, provides continuous lateral control (with a fixed authority) to keep the vehicle on a reference trajectory within the travel lane. Besides these systems, shared control (representing the adaptive co-pilot) is considered an adaptive authority that depends on the driver's state and the tracking performance, aiding the driver according to his/her needs of support. These modes are summarized in Table 7.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Manual Driving (MANUAL)** & **Lane Keeping (LK)** & **Lane Centering (LC)** & **Shared Control (SC)** \\ \hline No torque is applied by the automation. The driver only feels the self-aligning torque. & When the vehicle approaches the border line, the vehicle intervenes, applying a momentary torque. & A continuous torque is applied to keep the vehicle on a reference trajectory within the lane. & If the driver is attentive, they receive minimal correction torque, which only increases when getting close to the borders. If the driver is distracted, the authority increases and the free moving range is reduced. \\ \hline \(\lambda_{\text{dim}}\)\(=0\) Nm & \(\lambda_{\text{dim}}\)\(=0\) Nm & \(\lambda_{\text{dim}}\)\(=3\) Nm & \(\lambda_{\text{dim}}\)\(=FIS_{a}\)\(\leq\infty\) \  
In the experimental procedures, the tests are performed by the driver interacting with the vehicle only through the motorized steering wheel, while the longitudinal control is resolved by the adaptive cruise control. They consist of a 6 min highway driving situation (with minimum curvature radio of 420 m), at 85 km/h, with periodic distraction events (each 20 s).