## 4 Expressway PTV Detection Algorithm for Over-the-Horizon
### Data Preprocessing
#### 4.3.3 Construction of Section Traffic Flow Dataset  
Section traffic flow refers to the number of vehicles passing through the same road section (in the same direction) within a certain period of time. In the statistics of traffic flow in the expressway sections, we use the converted coefficient traffic flow for subsequent dynamic PTV detection. Due to significant differences in the performance and space occupied by vehicles of different models on the road, their level of danger may also vary. When analyzing and comparing complex traffic flows, it is necessary to perform equivalent conversions for different vehicle models. The introduction of the equivalent conversion coefficient can enable vehicles of different vehicle types to be compared and counted in the same \"unit\", making it easier to calculate traffic flow in sections. According to the latest standard vehicle classification for expressway tolls in 2019, vehicles can be divided into three categories: passenger car, truck, and special operation vehicle, of which passenger cars can be divided into 4 subcategories, and trucks and special operation vehicles can each be divided into 6 subcategories, for a total of 16 models, which correspond one-to-one with the code names of the charging models in the ETC transaction flow data. Among these, codes 1-4 indicate four categories of passenger cars, 11-16 indicate six categories of trucks, and 21-26 indicate six categories of special operation vehicles. In order to carry out the conversion, it is necessary to determine the conversion coefficients for other vehicles based on the JTG B01-2014 Technical Standard of Expressway Engineering and the data provided by Fujian Expressway Information Technology Co., Ltd. (Fuzhou, China), with small passenger cars as the standard cars [34]. It should be noted that the calculation method of the equivalent conversion factor may be slightly different due to factors such as region and industry, which need to be based on local standards and the actual situation. Table 1 shows the conversion factors for different vehicle types for comparison and analysis. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fee Code** & **Vehicle Description** & **Category** & **Subcategory** & **Conversion Factor** \\ \hline \multirow{3}{*}{1} & \multicolumn{2}{c}{H \(\leq\) 9 persons, L \(<\) 6000 mm} & \multirow{3}{*}{Class I} & 1 \\  & passenger car & & & \\  & H = 10-19 persons and L \(<\)6000 mm & & & \\  & passenger car & & & \\  & passenger car & & & \\  & H \(\leq\) 39 persons and L \(\geq\) 6000 mm & & & \\  & passenger car & & & \\  & H \(\geq\) 40 persons and L \(\geq\) 6000 mm & & & \\  & passenger car & & & \\ \hline \multirow{3}{*}{11} & \multicolumn{2}{c}{Z = 2, L \(<\) 6000 mm} & \multirow{3}{*}{Class I} & 1 \\  & \multicolumn{2}{c}{M \(<\) 4.5 t} & \multirow{3}{*}{Class II} & 1 \\  & \multicolumn{2}{c}{Z = 2, L \(\geq\) 6000 mm} & \multirow{3}{*}{Class II} & 1.5 \\  & \multicolumn{2}{c}{M \(>\) 4.5 t} & \multirow{3}{*}{truck} & \multirow{3}{*}{Class III} & 3 \\  & \multicolumn{2}{c}{Z = 3} & & \\  & \multicolumn{2}{c}{Z = 4} & \multirow{3}{*}{Class IV} & 3 \\  & \multicolumn{2}{c}{Z = 5} & \multirow{3}{*}{Class V} & 4 \\  & \multicolumn{2}{c}{Z = 6} & \multirow{3}{*}{Class VI} & 4 \\ \hline \multirow{3}{*}{21} & \multicolumn{2}{c}{Z = 2, L \(<\) 6000 mm} & \multirow{3}{*}{Class I} & 1 \\  & \multicolumn{2}{c}{Z = 2, L \(\geq\) 6000 mm} & \multirow{3}{*}{Class II} & 1.5 \\  & \multicolumn{2}{c}{M \(\geq\) 4.5 t} & \multirow{3}{*}{Special} & \multirow{3}{*}{Class II} & 1.5 \\  & \multicolumn{2}{c}{Z = 3} & & \\  & \multicolumn{2}{c}{Z = 4} & \multirow{3}{*}{Vehicle} & \multirow{3}{*}{Class IV} & 3 \\  & \multicolumn{2}{c}{Z = 5} & \multirow{3}{*}{Class V} & 4 \\  & \multicolumn{2}{c}{Z = 6} & \multirow{3}{*}{Class VI} & 4 \\ \hline \hline \end{tabular} H represents the authorized number of passengers, L represents the length of the vehicle, M represents the maximum allowable total mass, and Z represents the total number of axles.  
\end{table}