## 5 Experimental Results and Analysis
### Over-the-Horizon PTV Perception Algorithm
#### 5.4.1 Over-the-Horizon Perception Range Division
\begin{table}
\begin{tabular}{c c} \hline
**Data Distribution** & **Traffic Speed (km/h)** \\ \hline Maximum & 136.21 \\
75 th percentile & 102.71 \\ Average & 95.68 \\
25 th percentile & 84.23 \\ Minimum & 60.63 \\ \hline \end{tabular}
\end{table} 
Table 17: Vehicle speed distribution table. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **1 km** & **2 km** & **3 km** & **4 km** & **5 km** & **6 km** \\ \hline
10 km/h & 6 m & 12 m & 18 m & 24 m & 30 m & 38 m \\ \hline
30 km/h & 2 m & 4 m & 6 m & 8 m & 10 m & 12 m \\ \hline
50 km/h & 1.2 m & 2.4 m & 3.6 m & 4.8 m & 6 m & 7.2 m \\ \hline
60 km/h & 1 m & 2 m & 3 m & 4 m & 5 m & 6 m \\ \hline
80 km/h & 0.75 m & 1.5 m & 2.25 m & 3 m & 3.75 m & 4.5 m \\ \hline \end{tabular}
\end{table} 
Table 18: Schedule of two vehicles meeting. After detecting a PTV, it is necessary to update the vehicle location information in real time and provide the information to the driver in time. However, only when the vehicle passes through the ETC gantry and generates transaction data can the location information of the vehicle be obtained at the current moment. When the vehicle is passing through QD's Node\({}_{1}\) before reaching Node\({}_{2}\), the platform is unable to accurately monitor the location of the vehicle. Therefore, the distribution interval of ETC gantries directly affects the vehicle location refresh, and if the ETC gantries' distribution interval is too large, the vehicle location refresh is not timely. Therefore, it is necessary to analyze the impact of ETC gantry distribution interval on the provision of potentially dangerous vehicle information. Table 19 analyzes the refreshing time of different types of vehicle positions at different gantry intervals, and the refreshing time of vehicle positions is expressed as the time of a vehicle passing the section. According to the data in Table 19, if the gantry distribution interval is 1 km, the time for Class I passenger cars to pass through a section is 32.723 s, which means that the position of Class I passenger cars will be refreshed every 32.723 s. Similarly, the positions of other passenger cars, trucks, and special operation vehicles will be refreshed at 40 s and 45.004 s, respectively. According to the analyzed meeting schedule of two vehicles, it can be observed that the maximum speed difference is 80 km/h, and the safe distance is 1 km, so it takes 45 s for two vehicles to meet. Therefore, the driver has enough time to make countermeasures after obtaining the position of the PTV. Then, the gantry distribution \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Class I Passenger Car** & **Other Passenger Car** &
\begin{tabular}{c} **Truck and Special** \\ **Operation Vehicle** \\ \end{tabular} \\ \hline
1 km & 32.723 s & 40 s & 45.004 s \\ \hline
2 km & 65.445 s & 80 s & 90.009 s \\ \hline
3 km & 98.167 s & 120 s & 135.013 s \\ \hline
4 km & 130.89 s & 160 s & 180.018 s \\ \hline
6 km & 196.335 s & 240 s & 270.027 s \\ \hline \hline \end{tabular}
\end{table} 
Table 19: Traffic schedule of different types of vehicles at different gantry intervals. Figure 13: Comparison of the average speed of different vehicle types. interval of 1 km is within the feasible range. By the same token, 2 km is also within the feasible range. If the gantry distribution interval is 4 km, the time for Class I passenger cars to pass through a section is 130.89 s, and other passenger cars, freight cars, and special work vehicles are refreshed in 160 s and 180.018 s, respectively. According to the schedule of meeting two vehicles, the maximum speed difference is 80 km/h, and the safety distance is 4 km; then, it takes 180 s for two vehicles to meet, so the gantry distribution interval is 4 km in the feasible range. However, as for Gaode Map, the most professional Internet map maker in China, its car version displays the current real-time traffic condition information at a refresh frequency of once every 2 min.