## 5 Field Test Configuration and Results
### Results of Geometric Similarity Evaluation
#### 5.3.1 Results of Efficiency Evaluation
The high similarity observed in the lateral-motion scenarios is attributed to the fact that lateral motions, such as lane changes or curve driving, primarily depend on the proportional relationships between yaw rate, lateral acceleration, and steering angle. These relationships are influenced more by the vehicle's fundamental structure and tire characteristics than by speed changes. Additionally, under normal driving conditions, the tires operate within their linear response range, maintaining similar response characteristics at different speeds. Conversely, the lower similarity in the longitudinal-motion scenarios stems from physical characteristics related to acceleration and deceleration. As speed increases, the air resistance increases drastically, in proportion to the square of the speed, whereas the rolling resistance increases gradually, in proportion to speed. Furthermore, powertrain efficiency varies complexly with speed. Particularly at low speeds, the engine output is more sensitive to the vehicle's inertia, whereas at high speeds, it is affected more by the air resistance and control system delays. These factors increase the speed sensitivity of the vehicle's longitudinal behavior, resulting in the relatively low similarity indices observed. Notably, the integrated scenarios showed higher similarity indices than the longitudinal-motion scenarios, contrary to expectations. This is ascribed to the complementary nature of the complex vehicle behaviors. When longitudinal and lateral movements occur simultaneously, the extreme characteristics in each direction balance each other out, and complex movements trigger the intervention of the vehicle's stability control systems; thus, consistent movement is maintained despite speed variations. This inference highlights a paradoxical complexity-stability relationship, where single-behavior scenarios are more sensitive to speed changes than integrated-behavior scenarios, contradicting the general logic that system stability decreases with increasing complexity. The geometric similarity indices satisfying their respective evaluation criteria across all scenarios suggest that the credibility of the simulation platform within a given scenario \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Index**Scenario** & **A** & **B** & **C** & **D** & **E** & **F** & **Criterion** \\ \hline
81.11 & 80.86 & 76.09 & 75.43 & 78.09 & 76.52 & 71.68 (\(\mathbf{\alpha_{\mathrm{G}}}\)) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Geometric similarity for each scenario, along with evaluation criteria. could be assessed under a single representative speed condition. Thus, the proposed geometric similarity-based framework can considerably streamline the credibility verification process for XILS platforms. In summary, while all scenarios maintained adequate similarity across speed conditions, they exhibited distinct patterns correlated with vehicle dynamics principles. Based on this understanding, strategies can be developed to optimize testing efficiency while maintaining the credibility of XILS platforms.