# Measurement and Analysis of Vibration Levels for Truck Transport Environment in Korea
## 3 Results and Discussion
### Transport Vibration Level as a Function of Pavement Type and Travel Speed  
The effects of travel speed and pavement type on the truck transport vibration level were analyzed by extracting the time zone data corresponding to the truck's pre-planned travel speed and the pavement type from the vibration records measured on the test route configured for this study. Figure 6 and Table 5 show the vibration level according to the travel speed, with the vibration level increasing as the travel speed increased. Particularly in the low-frequency range of 1-10 Hz, the difference in the vibration level based on the travel speed clear (Table 6). These results are similar to those reported by other researchers [18; 21]. The increases in the vibration level of trucks with increases in travel speed indicate that the effects of road conditions on the truck's vibration level are more sensitive as the travel speed increases [18]. The increase rate of the vibration level according to travel speed in the air-ride truck was higher than that in the leaf-spring truck. This phenomenon is attributed to the more significant increase rate of the dynamic load acting on the air-ride truck as the travel speed increases, making the air-ride suspension stiffer. These results are similar to the research results of [PERSON] and [PERSON] [15], such that the air-ride suspension becomes thicker as the trailer load increases for air-ride trailers, resulting in higher vibration levels. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Kinds of Truck** & **Top 30\%** & **Lower 70\%** & **All Data** \\ \hline Leaf-spring 5-ton truck & 0.2878 & 0.1693 & 0.2119 \\ Air-ride 5-ton truck & 0.1808 & 0.0839 & 0.1075 \\ Leaf-spring 11-ton truck & 0.3410 & 0.1832 & 0.2385 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Overall rms G values of vertical PSD profiles for the three data selection methods in the frequency range of 1–250 Hz. Figure 7 shows the vibration levels of trucks according to the highway pavement type; the results of the analysis are shown in Tables 5 and 6. The vibration level of the air-ride truck within the overall frequency range of 1-250 Hz was approximately 50.0% on the concrete-surfaced highway and approximately 45.4% on the asphalt-surfaced highway compared with that of the leaf-spring truck. Moreover, the vibration level on the asphalt-surfaced highway was approximately 82.2% in the leaf-spring truck and approximately 74.5% in the air-ride truck compared with that on the concrete-surfaced highway. The difference in the vibration level by pavement type or suspension in the low-frequency range of 1-10 Hz showed the same tendency as that in the overall frequency range, although the difference was more significant. These results reflect the same travel speed in unloaded conditions; the results be different if the travel speed and payload are used as variables. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Kinds of Truck**} & \multicolumn{2}{c}{**Pavement Type**} & \multicolumn{2}{c}{**Travel Speed**} \\ \cline{2-5}  & **Concrete-Surfaced** & **Asphalt-Surfaced** & **30 \(\pm\) 10 km/h** & **60 \(\pm\) 10 km/h** & **90 \(\pm\) 10 km/h** \\ \hline Leaf-spring 5-ton truck & 0.1533 & 0.1421 & 0.0733 & 0.1174 & 0.1845 \\ Air-ride 5-ton truck & 0.0814 & 0.0640 & 0.0342 & 0.0600 & 0.0978 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The overall rms G values of vertical PSD profiles according to the pavement type and travel speed in the low-frequency range of 1–10 Hz. Figure 6: PSD plots for the vertical vibration levels according to the travel speed of the truck (**a**) leaf-spring 5-ton truck (**b**) air-ride 5-ton truck.