## 4 Results  
This study takes the FAW Jiefang J6M8\(\times\)4 series truck as an example, which were selected because they accounted for a large proportion of trucks in China at present and because of their high crash rate and their operational characteristics [52; 53]. For this type of truck, the first two axles are steering axles and they are the same in mechanical properties, and the last two axles are drive axles and they are the same in mechanical properties. Thus, the first and last two axles of this type of truck are regarded as the front and rear axles of the proposed model, respectively. This study performed calculations under different combinations of variables. 1. Prediction of truck skidding potential and recommendations of the MSBDRs on horizontal curves with different curve radii. The parameter values in the model are shown in Table 2.  
The results in Figure 9 show that:  
* During braking, there is a higher skidding potential of the rear axle compared to the front axle. In other words, the safety margin against skidding on front axle is met, but that of the rear axle is not necessarily met on horizontal curves during braking. * The curve radius has an effect on truck skidding. During braking, the smaller the radius of a horizontal curve, the higher the potential of skidding for trucks. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Influence Factor** & **Parameter** & **Symbol** & **Value** & **Unit** \\ \hline \multirow{4}{*}{Vehicle} & Mass & \(m\) & 30,000 & kg \\  & Height of the CG & \(h_{g}\) & 1.8 & m \\  & Synchronous adhesion coefficient & \(\vartheta_{0}\) & 0.4 & \\  & Front axle to CG distance & \(a\) & 3.60 & m \\  & Rear axle to CG distance & \(b\) & 4.25 & m \\ \hline \multirow{4}{*}{Road} & Design speed & \(V_{DS}\) & 120/100/80 & km/h \\  & Radius & \(R\) & 650/400/250 & m \\ \cline{1-1}  & Superelevation & \(i_{h}\) & 8 & \% \\ \cline{1-1}  & Downgrade & \(i\) & 0 & \% \\ \cline{1-1}  & Friction coefficient (tire-pavement) & \(\mu_{x,max}\) & 0.6 & \\ \hline Environment & Weather & & Dry & \\ \hline Driver behavior & Speed & \(V\) & 120/100/80 & km/h \\  & Deceleration & \(a_{x}\) & 0–5.5 & m/s\({}^{2}\) \\ \hline \multirow{4}{*}{Drive behavior} & Note: The blue-filled areas indicate that the impact of changes in these variables on truck skidding is being explored. \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \end{tabular}
\end{table} 
Table 2: Parameter values. Figure 8: Data analysis results for all highway sections. * In addition to emergency braking maneuvers, the horizontal curves designed in accordance with the current road geometry design standards, even with the limit-minimum radius, provide an adequate safety margin against skidding for trucks. * During emergency braking maneuvers, the horizontal curves designed in accordance with the current road geometry design standards pose a high potential of trucks skidding. The higher the deceleration, the higher the potential of skidding for trucks. * Therefore, taking into consideration the objective of ensuring safety and mitigating skidding risks, the recommended MSBDR is 4.5 m/s\({}^{2}\). It is worth mentioning that, in the calculation, the radius of horizontal curves was determined as the limit-minimum radius for each design speed selected, in accordance with the design criteria. The results obtained here should assure that, if a truck can brake on a limit-minimum-radius curve without loss of control, then that same truck will be able to brake on larger-than-limit-minimum-radius curves without loss of control. 2. Prediction of truck skidding potential and recommendations of the MSBDRs on horizontal curves with different slopes. The parameter values in the model are shown in Table 3.