# Do Heavy Vehicles Always Have a Negative Effect on Traffic Flow?
## 3 Characteristics of Traffic Flow
### Characteristics Analysis Result of Traffic Flow  
As shown in Figure 3 and Table 9, the traffic flow rate (converted from 5-min traffic volume to 1-h traffic flow rate) that distinguishes traffic jam from no traffic jam, and speed (average speed value of 5-min traffic flow) had a threshold of 2028 veh/h and 74.0 km/h, respectively. As shown in Table 9, when only passenger cars and small-sized heavy vehicles were included in the analysis, the thresholds were 2148 veh/h/ln for traffic flow rate and 79.8 km/h for speed, which were higher than when all vehicle types were included. This might be due to the relatively poor quality of traffic--in which the road was occupied by different types of vehicles, causing conflicts among the vehicles. This charac \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Classification** & **Vehicle Type** & **Example Vehicles** & **Application** \\ \hline
1 & 2-axis 1 unit & Passenger car & Small \\ \hline
2 & 2-axis 1 unit & Buses with \(\geq\)16 seats & Medium \\ \hline
3 & 2-axis 1 unit & Cargo trucks (\(\geq\)1–2.5 tons) & Small \\ \hline
4 & 2-axis 1 unit & Cargo trucks (\(\geq\)2.5-5 tons) & \\
5 & 3-axis 1 unit & Cargo trucks (5-5 tons) & Medium \\
6 & 4-axis 1 unit & Cargo trucks (tank lorry, dump, etc.) & \\
7 & 5-axis 1 unit & Cargo trucks (tank lorry, dump, etc.) & \\ \hline
8 & 4-axis 2 unit & Semi-trailers (flatbed semi-, tank lorry-trailers) & \\
9 & 4-axis 2 unit & Full trailers & \\
10 & 5-axis 2 unit & Semi-trailers (flatbed semi-trailers, etc.) & Large \\
11 & 5-axis 2 unit & Full-trailers (cargo full-trailers, etc.) & \\
12 & 6-axis 2 unit & Semi-trailers (flatbed semi-trailers, etc.) & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Classification and application of vehicle type [14]. Figure 3: Traffic flow rate (veh/h)–speed curve (km/h). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Classification** & **Maximum Flow Rate** & **Critical Speed** \\ \hline Small & 2148 veh/h/ln & 79.8 km/h \\ Mixed flow (Small + Medium) & 2052 veh/h/ln & 86.6 km/h \\ Mixed flow (Small + Large) & 2100 veh/h/ln & 76.7 km/h \\ All vehicles & 2028 veh/h/ln & 74.0 km/h \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Maximum flow rate and critical speed by vehicle classification. teristic was more apparent when it was compared with the characteristics of traffic flows in which only two vehicle types were present. Among the traffic having different vehicle types mixed, when small and medium-sized heavy vehicles were included, traffic volume and speed had a threshold of 2052 veh/h/ln and 74.0 km/h, respectively. When small- and large-sized heavy vehicles were included, the corresponding values were 2100 veh/h/ln and 76.7 km/h. In both cases, the thresholds were higher than those measured when all vehicle types were included. Such differences can be attributed to the driving patterns of each vehicle type. As shown in Table 10, the analysis of the speed distributions of small, medium, and large-sized heavy vehicles shows that the average speed was the highest for small and medium-sized vehicles (including passenger cars), while the variance and standard deviation of their speeds were higher than those of other vehicle types. This can be confirmed in Table 9, which shows that volumes of traffic flow reached the highest threshold only for the small-sized heavy vehicles. However, the larger standard deviations and variances in speed indicate that in the case of small-sized heavy vehicles, there were many cases of acceleration and deceleration while driving. In addition, if this happened in the basic section of the continuous traffic flow, it means that the driver tried to overtake other vehicles. In other words, small-sized heavy vehicles try to overtake a relatively large number of other vehicles, and when this happens, acceleration and deceleration occur more frequently, thus affecting the traffic flow to a greater extent.