# Classification of Speed Change and Unstable Flow Segments Using Geohash-Encoded Vehicle Big Data
## 4 Results and Discussion
### Interpretation of Results  
The velocity insights concerning Korean expressway segments are conventionally established through the concept of 'conzones,' wherein VDS facilitate the determination of instantaneous and average speeds within these delineated areas. A 'conzone' constitutes an expressway segment characterized by a consistent volume of passing vehicles, commonly associated with nodes such as interchanges, junctions, and toll gates. The particulars of this mechanism are exhibited in Table 7, which illustrates real-time data captured at 09:00 on 10 April 2018, encompassing various detectors and zones. VDS installations, spaced at irregular intervals spanning from 330 m to 2.96 km, engage in vehicle speed detection. Subsequently, the velocity data gleaned from two or more VDSs are amalgamated into an averaged ozone speed, imparting uniform interval-based information. Nevertheless, this approach falls short in accounting for instances such as accidents within a segment or the influence of subdivisions, thereby obscuring insights into UF occurrences. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Grid ID** & **TMS** & **SMS** & **Flow** & **Grid ID** & **TMS** & **SMS** & **Flow** & **Grid ID** & **TMS** & **SMS** & **Flow** \\ \hline  
F & 212300010310 & 104.85 & 104.82 & SF & 212310103130 & 103.25 & 103.25 & SF \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison of UF in the 12-step split grids for Expressway no. 50. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Count** & **VDS\_ID** & **Distance** & **VDS Zone** & **Conzone ID** & **Instantaneous Speed (km/h)** \\ \hline
1 & 0500 VDE00100 & 1.3 & 1240 & 0500 CZE010 \\
2 & 0500 VDE00200 & 2.3 & 1050 & 0500 CZE010 \\
3 & 0500 VDE00300 & 3.4 & 1300 & 0500 CZE010 \\
4 & 0500 VDE00400 & 4.9 & 850 & 0500 CZE010 \\
5 & 0500 VDE00500 & 6.05 & 2960 & 0500 CZE020 \\
6 & 0500 VDE00700 & 8.7 & 1340 & 0500 CZE025 \\
7 & 0500 VDE00800 & 9.9 & 740 & 0500 CZE025 \\
8 & 0500 VDE00900 & 11.3 & 2500 & 0500 CZE030 & 66 \\
9 & 0500 VDE01000 & 12.6 & 660 & 0500 CZE040 & 106 \\
10 & 0500 VDE01100 & 13.8 & 1300 & 0500 CZE040 & 126 \\ \(\vdots\) & \(\vdots\) & \(\vdots\) & \(\vdots\) & \(\vdots\) & \\
95 & 0500 VDE09400 & 109.9 & 1350 & 0500 CZE200 & 89 \\
96 & 0500 VDE09500 & 111.2 & 1950 & 0500 CZE200 \\ Minimum & & & 330 & 49 \\ Maximum & & & 2960 & 126 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Speed information guidance criteria for westbound segment of Expressway No. 50. The spatial domain under scrutiny encompasses the two-way traffic of Expressway no. 50 within Gyeonggi Province, characterized by a cumulative one-way expanse of 102.14 km. To derive segment speeds, the study employed DTG-based individual vehicle statistics. Segments featuring uniform speeds bereft of substantial inter-vehicle discrepancies underwent further partitioning into a geohash-derived grid, establishing a sense of uniformity, termed SF. In contrast, segments characterized by significant speed disparities among vehicles were systematically subdivided into smaller units designated as UF, until each grid reached a minimum size of 100 m. Notably, instances manifesting pronounced disparities in vehicle speeds, as illustrated in Table 8, were classified as UF segments. With UF segments thus identified, the intricate road network map was subsequently scrutinized to pinpoint influential variables. Figure 10 elucidates the outcomes of this analytical endeavor; the red line in the picture is the UF segments analysis result. This line matches the center line of the road, and the shape of the road matches the background of the map, highlighting distinct scenarios:  
1. UF emerges as a segment characterized by a mixture of vehicles undergoing speed reduction before the expressway toll plaza, intermingled with those maintaining high velocities, yielding an average speed of 51 km per hour. 2. The UF category is typified by an average speed range of 66-67 kph, wherein vehicles of varying velocities merge from the right. 3.