## 5 Contributions and Limitations
Each alternative was assessed against comprehensive criteria, including horizontal and vertical geometry, flood risk, rock hardness, and fracture density. These criteria are quantified using specific design parameters and risk factors, ensuring a detailed and objective assessment of each alternative. The threat score (\(TS\)) for each road segment was calculated using a weighted combination of design parameters, allowing normalization and comparison of the alternatives based on their overall risk and suitability. Ultimately, alternatives with the lowest average threat scores in each segment were connected to form the preferred alignment, which showed a significant reduction in safety risks and hydrological and geological impacts. The process allowed for iterative refinement, where initial evaluations can lead to adjustments and improvements in the alternatives, further enhancing the outcome. The comparison between alternatives demonstrated that alignment enhancements included eliminating horizontal curves with large radii and small deflection angles. Additionally, consecutive reverse curves were refined by increasing radii and the length of tangents between them to achieve better risk intensities for design parameters, as outlined in Table 1. Hence, radii exceeding 1000 m (when feasible) were utilized instead of sharp curves with smaller radii less than 1000 m.  
The heterogeneity of surface and subsurface rock formations, especially in mountainous areas, significantly influenced the selection of a less hazardous and safer path. The litho-properties of the terrain help in determining the optimal route. Hard basement rocks scoring between 5 and 10 and sedimentary bedding scoring between 1 and 4, characterized by being massive, compact, and homogeneous, pose very high to highly vulnerable risks to road design. The distribution and density of lineaments, such as faults, joints, and foliations, are key geoenvironmental factors considered in selecting the route with the lowest threat scores. Overall, the methodology used in this study is considered comprehensive due to consideration of the road, the driver, and the environment (in terms of hydrological and geological aspects). The methodology can be applied to the design of any type of road and can be tailored to specific design speeds or environments. The proposed methodology provides a valuable tool for engineers and policymakers to ensure the sustainable construction of safe and resilient transportation infrastructure in challenging environments and represents the best solution from both practical and engineering perspectives. There are, however, several limitations that need to be considered in the future enhancement of the methodology. First, route selection is not applied using an optimization formulation of a model, such as the research presented by [PERSON] et al. [6]. Future work in this methodology will include using a 3-D approach to automate road alignment optimization instead of comparing between feasible alternatives. In addition, a broader analysis using genetic algorithms and path optimization methods could help refine the tool. Second, restricted sight distance should be added to the risk factor parameters and analyzed when choosing alternatives. Third, a design consistency approach could be incorporated into the risk factor parameters used in the analysis. Additionally, the method proposed is limited to zones without special environmental fragility or protection. Even though the cost was considered implicitly in the type of rocks excavated, a more explicit approach would be beneficial in future work, with the cost added as a factor. Moreover, the study primarily focused on avoiding extensive excavation to mitigate rockfall hazards, as mountainous roads typically follow the natural alignment of streams. The risk of rockfalls caused by excavation through the mountains was inherently considered a threat score based on geological factors. A detailed examination of dragging cases along the crossing wades has not been included.