## 3 Results
### Quantitative Evaluation (Experimental Results)  
Exploratory studies were performed with five drivers (one woman and four men), aged 21 to 49 years (mean = 30.2, SD = 10.8), with at least 3 years of driving experience (mean = 11.8, SD = 10.9), including occasional (1), frequent (1), and regular (3) drivers. All have some degree of relation with automated driving R&D activities. Figure 8 shows typical driver behavior using the four driving modes. The lateral error graphic (Figure 8a) shows that in MANUAL and LK modes, the driver repeatedly departs from the lane center during the distraction events, though the LK effect of avoiding the lane departure is efficiently achieved. Results also indicate that the distraction events during higher road curvature sections (Figure 8d) produced larger deviations. On the contrary, LC and SC do not show a significant difference between straight and curved segments, and overall, both seem to behave similarly, achieving the goal of keeping the vehicle close to the lane center. In terms of effort, the driver applied the highest torques when driving in MANUAL and LK modes (Figure 8c). While in MANUAL, most of the torque is applied to return the vehicle to the lane center when large deviations occur; in LK, the driver torque increases by the \"bump\" effect produced when the vehicle reaches the lane limits (Figure 8f). On the other hand, at first sight, SC seems to produce lower efforts compared to LC (Figure 8c,e), but due to the lack of visible significant difference in terms of effort, the analysis will be performed quantitatively. Figure 8b,e show the signal of the DMS during one distraction event (DE), and the authority calculated by the FIS system. Figures 9-14 show the performance of each driving mode, separating the time spent within the distraction event window (of 10 s as shown in Figure 7) and out of it (normal driving). Figures 9, 10, 13 and 14 compile the tracking (lateral and angular) errors and (driver and automation) driving efforts, respectively. The overall (combining all drivers) RMS values are shown in color, while the respective maximum values are depicted by the white bars. The individual RMS and MAX values for each driver are shown by color and black crosses (+) to evaluate the data dispersion. Note that RMS values are considered deviations from the road center (i.e., they are not standard deviations around the mean), thus, they also reflect the effects of the bias tracking errors. Figures 11 and 12 show safety indicators: Figure 11 shows RMS and MIN TLC; Figure 12 shows the percentage of time spent with a TLC below a 3.8 s (safety) threshold. Figure 8: Typical driver behavior under the four tested driving modes (data from one driver). Figure 11: Safety indicators statistics (RMS and MIN of TLC). Figure 9: Tracking error statistics (RMS and MAX of lateral error). Additionally, performance indicators of the LC controller, when allowed to control the vehicle without driver intervention (referred to in graphics as Automation-only), are provided to validate the controller and for comparison purposes. The controller shows efficient lateral and angular tracking performance, with an RMS on the lateral error of 6 cm and MAX value of 11 cm, and an angular deviation below 1.5 deg., which are positive  
Figure 14: Driving efforts statistics (RMS and MAX of automation’s torque). Figure 12: Safety indicators statistics (% of time under TLC-threshold). Figure 13: Driving efforts statistics (RMS and MAX of driver’s torque). results for a reference tracking controller. In terms of safety, the TLC is always over 3.8 s (this value is used as the safety threshold for the comparison of the TLC under the four driving modes). Concerning the controller efficiency, automation torque RMS is close to 0.5 Nm, and the MAX value is around 1.5 Nm (applied during the highest curvature section). The lateral and angular errors (Figures 9 and 10) show that all three tested driving aids significantly improve the ability to track the road center trajectory with respect to the MANUAL driving mode.