## 4 Study Area and Data Description  
The two-lane rural road network in the state of Oregon was investigated as a case study in order to validate the proposed method. A total roadway segment sample of around 1495 miles from the eastern and western region was used in this investigation to ensure adequate geographic coverage. The study sample included roadways from different parts of the state as shown in Figure 1. In general, roadways in the eastern part of the state run in flatter terrain with less restrictive alignment, while those in the western part of the state run in mountainous terrain with more restrictive alignment (winding routes, sharp radii, etc.). All state-owned rural two-lane roads were identified using online geographic information system (GIS) data [18]. The roadway segments were then selected from the collection to obtain sample data ensuring sufficient geographical coverage. Data were collected for roadway segments using 0.05-mile increments to ensure that data would capture all changes in the physical characteristics of the roadway, thus eliminating the possibility of missing significant differences between consecutive observation points. The posted speed limit in all the segments considered for this study is 55 mph. Intersections and 0.05-mile segments along upstream and downstream approaches were excluded from the dataset. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Risk Factors**} & \multicolumn{2}{c}{**Approximate Ranges of**} & \multirow{2}{*}{**Categories**} & \multirow{2}{*}{**Terms**} \\  & & **Variables** & & \\ \hline Segment Length (SL) & \multicolumn{3}{c}{Exact Length} \\ \hline \multirow{2}{*}{Lane Width (LW)} & LW \(<\) 11 & 1 & Narrower \\ \cline{2-4}  & LW \(\geq\) 11 & 2 & Wider \\ \hline \multirow{2}{*}{Shoulder Width (SW)} & SW \(<\) 1.8 & 1 & Narrower \\ \cline{2-4}  & SW \(\geq\) 1.8 & 2 & Wider \\ \hline \multirow{2}{*}{Degree of Horizontal Curvature (DC)} & DC \(=\) 0 & 0 & Straight \\ \cline{2-4}  & DC \(<\) 10 & 1 & Mild \\ \cline{2-4}  & 10 \(\leq\) DC \(<\) 27 & 2 & Moderate \\ \cline{2-4}  & DC \(\geq\) 27 & 3 & Sharp \\ \hline \multirow{2}{*}{Grade (G)} & G \(<\) 4 & 0 & Mild \\ \cline{2-4}  & G \(\geq\) 4 & 1 & Steep \\ \hline \multirow{2}{*}{Driewway Density (DD) (driveways per mile)} & \multicolumn{3}{c}{Exact Number} \\ \hline \multirow{2}{*}{Side Slope (SS)} & Steep & 1 & Steep \\ \cline{2-4}  & Moderate & 2 & Moderate \\ \cline{2-4}  & Flat & 3 & Flat \\ \hline \multirow{2}{*}{Fixed Objects (FO)} & Many & 1 & Many \\ \cline{2-4}  & Some & 2 & Some \\ \cline{2-4}  & Few & 3 & Few \\ \hline \multicolumn{2}{c}{Volume (V)} & Exact Volume \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Explanatory variables of proposed model [9]. The Oregon Department of Transportation (DOT) online databases and video logs were used to identify and compile traffic, roadway geometry, roadside, and crash data [19; 20]. The roadway geometric data includes lane width, shoulder type and width, horizontal curve presence degree of curvature, length of the horizontal curve, spiral curve presence and length, vertical curve presence and type, grade, and length of vertical curve. Roadside characteristics consists of driveway density, side slope ratings, and fixed object ratings. These two factors are taken from the Oregon DOT online database and video logs, respectively, both at 0.05-mile increment. Crash data for ten years (2011-2020) were collected for the study sample using the Oregon DOT online database [20]. Data on more than 20 individual crash characteristics-including crash location, road character, impact location, traffic control, crash type, crash severity, vehicle type, and weather condition were collected and combined with the geometric and roadside database forming an integrated dataset for analysis. Traffic data from 2011 to 2020 were also collected separately and compiled to the study integrated dataset described earlier.