## 2 Materials and Methods
### Data Sources
Therefore, the dummy variables are generated using one-hot encoding for each categorical variable. As a result, Terrain, Type of Shoulder, Median Type, and Land-use variables were regenerated as 3, 4, 5, and 8 dummy variables, respectively, and 37 variables were used for analysis as explanatory variables. \begin{table}
\begin{tabular}{l c c} \hline \hline \multicolumn{1}{c}{**Information**} & \multicolumn{1}{c}{**Highway with Two-Lane**} & \multicolumn{1}{c}{**Highway with Multi-Lanes**} \\ \hline Average Daily Traffic Volume & 3494 veh/day & 19,976 veh/day \\ \hline Average Length of Segments (m) & 181 & 172 \\ \hline \multirow{3}{*}{Number of Road Segments} & Total & 1918 (100\%) & 998 (100\%) \\  & Road Segments with Curves & 1893 (98.7\%) & 913 (91.5\%) \\  & Road Segments without Curves & 25 (1.3\%) & 85 (8.5\%) \\ \hline Average Lane Width (m) & 3.45 & 3.77 \\ \hline Average Shoulder Width (m) & 1.03 & 1.31 \\ \hline Average Density of Driveway (No./km) & 3.64 & 2.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Information about road segments. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Classification** & **Geometric Conditions** & **Roadside Design** & **Traffic Conditions** & **Others** \\ \hline \multirow{3}{*}{Variables} & Radius, grade, lane width, segment length, driveway, and shoulder & Median; lighting & Speed limit, ADT, and speed control system & Terrain, land-use, bus-stop, and delineation \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Variables for intersections and rural road segments. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & **Name** & **Variable Description** & \begin{tabular}{c} **Statistical Description** \\ **Min.** \\ \end{tabular} & \begin{tabular}{c} **Max.** \\ \end{tabular} \\ \hline \multirow{3}{*}{\begin{tabular}{c} Dependent \\ variable \\ \end{tabular} } & Traffic accident (crash) & \begin{tabular}{c} V2V collision \\ [occurred = 1, not occurred = 0] \\ \end{tabular} & 0 & 13 \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Exploratory \\ variables \\ \end{tabular} } & Traffic volume & Average daily traffic volume [veh/day] & 4961 & 43,992 \\ \cline{2-4}  & Heavy traffic volume & Average daily heavy vehicle volume [veh/day] & 517 & 4342 \\ \cline{2-4}  & Length & Length of road link [m] & 25 & 850 \\ \cline{2-4}  & Existence of H. Curve & The existence of a horizontal curve (dummy) & 0 & 1 \\ \cline{2-4}  & Existence of v. curve & The existence of a vertical curve (dummy) & 0 & 1 \\ \cline{2-4}  & Radius & Length of horizontal curve [m] & 0 & 6800 \\ \cline{2-4}  & Approaching slope & Vertical slope [\%] & \(-10\) & 7 \\ \cline{2-4}  & The number of lanes & The number of lanes & 0 & 5 \\ \cline{2-4}  & The number of light & The number of lighting facilities & 0 & 16 \\ \cline{2-4}  & Terrain & Type of terrain [level, rolling, and mountainous] & 1 & 3 \\ \cline{2-4}  & Lane width & Lane width [m] & 11.2 & 45 \\ \cline{2-4}  & Shoulder width & Shoulder width [m] & 0 & 5 \\ \cline{2-4}  & Type of shoulder &
\begin{tabular}{c} Type of shoulder [Non = 0, pavement = 1; \\ non-pavement = 2; others = 3] \\ \end{tabular} & 0 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Descriptive Statistics. Figure 2: Segmenting method for rural road segments. The dependent variable in this study is binary, with values representing whether an accident occurred (coded as 1) or did not occur (coded as 0) on a given road segment within a specified time frame. While accident occurrences were directly obtained from the national police agency data, segments without recorded accidents were assumed to have 'no accident' occurrences. This approach allowed us to examine roadway characteristics on segments where accidents were either present or absent, which is critical for balanced modeling. In summary, the dataset is structured at the road segment level, with each segment characterized by a range of variables, including the average daily traffic volume, geometric conditions, and accident occurrence status.