# Classification of Speed Change and Unstable Flow Segments Using Geohash-Encoded Vehicle Big Data
## 4 Results and Discussion  
### Analysis Results  
The DTG data sourced from freight vehicles along the Interstate 50 corridor facilitated the acquisition of comprehensive individual vehicle information traversing the expressway. Extracting data from peak traffic periods demonstrated noteworthy fluctuations in speed homogeneity across distinct timeframes. Notably, Tuesday registered the lengthiest average trip duration of 339.5 min, coupled with the shortest average journey distance of 165.1 km. Consequently, data from Tuesday at 9:30 a.m.--falling within the peak hour range of 8:00 a.m. to 10:00 a.m., a period characterized by heightened truck activity--was selected for further analysis. Raw data fields from truck DTGs underwent preprocessing, with the encrypted trip key and chassis number serving as criteria for bulk elimination of erroneous entries. Paramount data for this study encompassed vehicle speed, vehicle position, and GIS azimuth angle fields, with the 'TIME' field employed to facilitate time-based filtering. The outcome of the 12-step grid partitioning of the Gyeonggi region along Expressway no. 50, as executed using the geohash algorithm with DTG data, is visually presented in Figure 7. If it is located above the standard deviation relationship curve between SMS and TMS, it is classified as SF, and if it is located below, it is classified as UF and the space is separated repeatedly. Figure 8 delineates the resultant 12-step grid division for the eastbound Expressway no. 50 in Figure 8a, road line configurations and overlapping segmentation in Figure 8b, and the extraction of the unstable traffic component within the final 12 segments in Figure 8c. A parallel analysis conducted on Interstate 50's westbound trajectory is showcased in Figure 9. Table 5 comprehensively encapsulates the statistics derived from this analysis. Here, the part where the matched road alignment was cut off was excluded due to insufficient data for analysis. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Expressway**} & \multicolumn{2}{c}{**Data Fields**} \\ \cline{2-5}  & **Node** & **Link** & **Field Name** & **Attribute** & **Value** \\ \hline \multirow{3}{*}{Nationwide} & \multirow{3}{*}{4501} & \multirow{3}{*}{9835} & LINK\_ID & Link ID & Digit (2440063100) \\  & & & LANES & Number of lanes & Digit (5) \\ \cline{1-1}  & & & ROAD\_NO & Road number & Digit (1) \\ \hline \multirow{3}{*}{Gyeonggi-do} & \multirow{3}{*}{951} & \multirow{3}{*}{2133} & ROAD\_NAME & Road name & Text (Youngdong) \\ \cline{1-1}  & & & CONNECT & Link & Digit (000/101) \\ \cline{1-1}  & & MAX\_SPD & Maximum speed limit & Digit (110 km/h) \\ \cline{1-1}  & & LENGTH & Link length & Digit (344.7723755 km) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Node-link data definition. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time** & 1–30 April 2018 & **Region of Interest (Road)** & Expressway No. 50 in Gyeonggi-do \\ \hline \multirow{3}{*}{**Data Size**} & Approx. 3.13 TB & **Number of** & 2775 \\  & (Approx. 22.35 billion files, intervals of 1 s) & **Vehicles** & **2775** \\ \hline \multirow{6}{*}{**Data Fields**} & **Field Name** & **Attribute** & **Note** \\ \cline{2-4}  & T\_KEY & Trip key & Encoding \\ \cline{1-1}  & CARNUM & Car number & Encoding \\ \cline{1-1}  & SPEED & Vehicle speed & km/h \\ \cline{1-1}  & WGS84\_X & Vehicle location X & Latitude coordinate (WGS84) \\ \cline{1-1}  & WGS84\_Y & Vehicle location Y & Longitude coordinate (WGS84) \\ \cline{1-1}  & AZIM & GIS azimuth & Degree \\ \cline{1-1}  & TIME & Time & Date-hour-minute-second (18042809074000) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: DTG data definition. Figure 8: Eastbound UF results for Expressway No. 50. Figure 7: Comparison of TMS, SMS, and UF boundaries in the12-step grid split result. The segmentation results encompassing 301 segments, stemming from the 12-fold division of 188 grids, identified outliers beyond the standard deviation threshold.