## 3 Results
### Evaluation of Operator Comfort  
Driving surface roughness is one of the major factors affecting vibration exposure significantly. According to Equation (1) and other obtained data, the roughness of the soil surface, unpaved road, and asphalt road were 1.11, 1.15, and 1.19 mkm\({}^{-1}\), respectively. The standard United States IRI thresholds range from 1.5 to 2.68 mkm\({}^{-1}\) for all kinds of roads, and IRI < 1.5 mkm\({}^{-1}\) is considered as a good road segment [59; 60]. The calculated IRI of this study was lower than the standard range, which indicates a good condition of the driving surfaces. As the tests were conducted in the machinery testing beds of the TYM Tractors (TYM Tractors, Co., Ltd., Iksan, Republic of Korea), the homogenous condition of the driving surfaces of this study might be the possible reason behind this low roughness. Figure 6 shows the maximum level of vibration measured at the operator's seat frame under different driving surfaces, operating statuses, and load conditions regarding the three translational axes (X, Y, and Z). Vibration exposures at the Z-axis were very low (0.15-0.20 ms\({}^{-2}\)) compared to the X-axis (8-12 ms\({}^{-2}\)) and Y-axis (5-8 ms\({}^{-2}\)) for all conditions, due to the absence of a suspension system. More specifically, the selected  
Figure 4: Vibrational exposures of the conveyor belt, dibbling part-1, and dibbling part-2 for different load conditions under high (**a**,**b**) and low (**c**,**d**) driving speeds during transplanting. The considered ELV was 2.5 ms\({}^{-2}\). Figure 5: Onion seedlings were split from the track of the conveyor belt due to high vibrational exposure. The dotted line indicates the track position, and the arrow indicates the splitting directions. vehicle is manufactured as a rice transplanter, where a suspension system is not essential due to the soft driving surface (saturated soil). Generally, vibrational magnitudes vary depending on vehicle types, suspension systems, and driving surface. During driving on the soil surface, the vibration level was higher in the dynamic condition compared to the static condition. Some upland crop machinery, such as hand tractors, also produce similar vibration exposure. [PERSON] and [PERSON] (1986) observed 6.7-7.8 ms\({}^{-2}\) and 5.1-6.2 ms\({}^{-2}\) weighted vibration during rota-tilling and rota-pudding, respectively, at forward speed of operation from 0.30 to 0.63 ms\({}^{-1}\). An opposite scenario was observed during driving on the unpaved and asphalt roads for both unloaded and loaded conditions. Moreover, a small (1-2 ms\({}^{-2}\)) vibration difference was observed for 40 kg load difference (unloaded and loaded conditions) for all kinds of driving surfaces and operating statuses. Table 7 shows the evaluation of operator exposure based on ISO 2634-5 standards. Compared to the limits mentioned in the ISO (low (R\({}^{\text{A}}\) < 0.8), moderate (0.8 < R\({}^{\text{A}}\) < 1.2), and high (R\({}^{\text{A}}\) > 1.2)), the operator will face high health risk in all types of operations, especially on irregular surfaces (i.e., soil surface and unpaved road), as the minimum observed R\({}^{\text{A}}\) was 1.36.