# Analysis of Operating Safety of Tractor-Trailer under Crosswind in Cold Mountainous Areas
## 3 Analysis and Discussion of Driving Safety Results for Tractor-Trailers
### Analysis of Hazardous Conditions for Tractor-Trailers  
When the speed was increased to 40 km/h and the tractor-trailer was experimented with different side wind speeds, the simulation analyzed its operating state, at which point the Trucksim issued a warning that the hinge of the tractor-trailer exceeded a deflection of 500 mm, and it was found that the tractor-trailer had experienced a sideslip and a torsional folding phenomenon occurred. The distribution of the yaw rate and lateral acceleration under these conditions are shown in Figure 12; the vertical load and LTR values for different wind speeds are shown in Figure 13.  
It can be found from Figure 12a that when the tractor-trailer passed through the low adhesion road bend at the driving speed of 40 km/h, it started to slip after entering the bend, and the yaw rate reached the maximum at about 12 s, which was 12.95 deg/s (\(v_{\rm w}=62\) km/h), 12.90 deg/s (\(v_{\rm w}=68\) km/h), 12.80 deg/s (\(v_{\rm w}=74\) km/h), respectively. Additionally, in Figure 12b, it could be known that When a towed tractor-trailer skidded sideways, a sudden change in lateral acceleration occurred, that a sudden change in lateral acceleration was the sign that a sideslip had occurred. Additionally, an increase in wind speed did not affect the maximum of the ultimate lateral acceleration when sideslip, and the lateral accelerations at this point all exceeded 0.28 g, with a maximum of 0.284 g. At this time, the tractor-trailer had a serious sideslip, and it could not return to normal course by adjusting steering wheel angle. That gave a value of 0.284 g for the lateral acceleration of a tractor-trailer in the event of a severe accident on the cold mountainous road. In addition, it can be seen from the left and right load distribution of the vehicle in Figure 13b that the maximum LTR value was only 0.598 (\(v_{\rm w}=62\) km/h) even when the vehicle slipped out of the lane, which was still relatively safe for vehicle rollover instability. On the road with a low adhesion coefficient (\(\varphi=0.3\)), vehicle sideslip accidents occur preferentially compared with rollovers. From the above analysis it can be concluded that when the sideslip occurs, with the increase in wind speed, the vehicle rollover index LTR value decreases, and the vehicle yaw rate decreases, but the maximum value is still less than the safety theoretical value of the ordinary road 16.5 deg/s. On the one hand, the low adhesion coefficient of ice and snow  
Figure 12: (**a**) Yaw rate and (**b**) lateral acceleration of tractor-trailer for driving speeds over 40 km/h. Figure 13: (**a**) Lateral vertical load distribution and (**b**) LTR value of the left and right tire for driving speeds over 40 km/h. pavement reduces the safety threshold of vehicle sides lips. On the other hand, the effect of crosswind on vehicles also reduces the side slip threshold under the conditions of ice and snow pavement. Therefore, sideslip risk should be focused on this type of road condition. Setting the road adhesion coefficient \(\varphi=0.3\) in extreme weather conditions, road conditions for the curve radius \(R=60\)m without slope, by changing different crosswind conditions, to investigate the safe speed of tractor-trailer. The results of the simulation of the proposed maximum speed of the tractor-trailer with severe sideslip and just sudden changes in lateral acceleration are shown in Table 5.  
When the wind speed reached \(90\) km/h, even in a stationary state, the tractor-trailer had a sideslip displacement situation, while the safe speed under different crosswind conditions was reduced accordingly, as shown in Figure 14, so the recommended speed is limited to the green part and the critical speed is limited to the yellow part, when the speed reaches the yellow area, the tractor-trailer has a side slip, and when the speed reaches the red area, a serious side slip occurs.