# Analyzing Important Elements for Improving the Safety of Motorways
## 3 Data Description and Preprocessing
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Unit** & **Details** \\ \hline Frequency of Traffic Accidents (Accidents) & cases/year & Frequency of individual traffic accidents \\ \hline Truck Traffic Ratio (TruckRatio) & percent (\%) & Proportion of trucks in total traffic volume \\ \hline Slow Traffic Time (SlowTime) & hours/year & Total hours of slow traffic based on hourly travel speed (considered slow traffic if travel speed is between 40 km/h and 80 km/h) \\ \hline Congestion Duration (CongTime) & hours/year & Total hours of congestion based on hourly travel speed (considered congested if travel speed is below 40 km/h) \\ \hline Number of  Hazardous Driving Behaviors (HazardousBehavior) & cases/year & Total frequency of 11 types of hazardous driving behaviors \\ \hline Conzone Length (CongLength) & meters(m) & Length of the conzone \\ \hline Hazardous (LongSlopeRatio) & percent (\%) & The proportion of sections with longitudinal slopes surpassing the hazardous condition threshold is a critical metric. According to the “Road Structure and Facility Standards” of Korea, the maximum longitudinal slope permitted for highways is elaborated in Table 3. For the purposes of this study, the hazardous condition threshold is defined as slopes exceeding 6\% \\ \hline Hazardous Curve Radius Ratio (CurveRadiusRatio) & percent (\%) & The proportion of sections with curve radii surpassing the hazardous condition threshold is a crucial parameter. As per the \"Road Structure and Facility Standards\" of Korea, the minimum curve radius allowed for highways is outlined in Table 4. For this study, the hazardous condition threshold is defined as curve radii less than 500 m \\ \hline Fog-Prone Section Ratio (FogProneRatio) & percent (\%) & Proportion of fog-prone sections \\ \hline Ice-Prone Section Ratio (IceProneRatio) & percent (\%) & Proportion of ice-prone sections \\ \hline Snow-Prone Section Ratio (SnowProneRatio) & percent (\%) & Proportion of snow-prone sections \\ \hline Number of Lanes (Lanes) & Lanes & Number of lanes in the conzone \\ \hline Total Traffic Volume (TotalVolume) & vehicles/day & Annual average daily traffic (AADT) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Data derivation method used for analysis. The \"Number of Hazardous Driving Behaviors\" was computed using data obtained from digital tachyographs (DTGs) installed on buses and trucks. Based on statistical correlations with traffic accidents, the \"Number of Hazardous Driving Behaviors\" was defined across 11 types [28]. These 11 types encompass speeding, prolonged speeding, rapid acceleration, rapid start, rapid deceleration, sudden stop, abrupt lane change, sudden overtaking, sharp left turn, sharp right turn, and sharp U-turn. Before commencing the analysis, data preprocessing steps were executed on the provided dataset. Two primary preprocessing techniques were applied: elimination of data with missing values and min-max data scaling. Studies have established that a substantial proportion of missing data in an analytical dataset can adversely affect the model's performance [29]. Upon scrutinizing the dataset for missing values, it was noted that some data points for the Truck Traffic Ratio (TruckRatio) were absent. Conzones with missing data were excluded from the analysis, resulting in a final preprocessed dataset size of 1120. The outcomes of the basic statistical analysis of these 1120 data points are detailed in Table 5, with the data distribution visually depicted in Figure 1. \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Design Speed (km/h)**} & \multicolumn{3}{c}{**Applied Maximum Superelevation**} \\ \cline{2-4}  & **6\%** & **7\%** & **8\%** \\ \hline
120 & 710 & 670 & 630 \\ \hline
110 & 600 & 560 & 530 \\ \hline
100 & 460 & 440 & 420 \\ \hline
90 & 380 & 360 & 340 \\ \hline
80 & 280 & 265 & 250 \\ \hline \end{tabular}
\end{table} 
Table 4: Criteria for the minimum plane curve radius (m) of motorways in Korea.