# Analysis of Operating Safety of Tractor-Trailer under Crosswind in Cold Mountainous Areas
## 1 Introduction  
With the development of e-commerce, the demand for logistics transport is growing, and the tractor-trailer has a large loading capacity, so that it accounts for an increased proportion of cargo transport vehicles, but because of its high centre of gravity, large volume, and the interaction between tractor and trailer interactions, and other characteristics [1], when driving in the mountain highway, vulnerable to road alignment, crosswind and other factors. In particular, in the complex mountainous terrain, the crosswind has a significant acceleration effect impact [2, 3], in addition to the low adhesion coefficient of snow and ice in winter, tractor-trailer driving safety hazards are great. In addition, once an accident occurs, the tractor-trailer will cause great economic losses, especially in mountainous sections, which will easily cause secondary accidents and traffic jams. According to the U.S. Department of Transportation Bureau of Hazardous Materials Safety, statistics show that each year the tank semi-trailer in the transport process led to traffic accidents of about 16,000-20,000 [4]: Chinese automobile safety transport accident statistics also show: the proportion of major traffic accidents due to lateral instability is around 90% [5]. Therefore, in order to reduce accidents or reduce the severity of accidents of tractor-trailers, their driving characteristics in complex environments need to be analyzed. In terms of crosswinds affecting the operational safety factors of tractor-trailers, experts, and scholars have conducted research in terms of road conditions [6, 7], crosswind conditions [8], and complex environments [9, 10]. [PERSON] et al. found that different roadradio and wind deflection angles have the greatest impact on the safety of tractor-trailer driving in a conventional road environment [11]. In the early years, [PERSON] et al. [12; 13; 14] investigated the safety of a range of vehicles travelling on roads in crosswind conditions, while defining three types of accidents due to wind based on analysis results: overturning, sideslip, and excessive rotation. Later, many scholars have studied different road environments through wind tunnel experiments, based on the studies of [PERSON] et al. For example, [PERSON] [15] found that compared with ordinary roads, tractor-trailers are more likely to have lateral instability on long-span bridges. [PERSON] et al. [16] conducted a series of wind tunnel tests on various large vehicles (a van, a bus, and a lorry) driving on long-span bridges. The results show that lorry has become the most affected by crosswinds because of the highest rolling moment coefficient. [PERSON] [17] focused on the aerodynamic characteristics of different vehicles under different wind flow conditions (smooth flow, turbulent flow, and boundary layer flow) through a wind tunnel. The results show that the center of gravity of the vehicle will significantly affect the aerodynamic characteristics of the vehicle, and further point to the driving safety problem for large vehicles, such as heavy trucks. [PERSON] [18] analyzed the potential possibility of truck rollover by crosswind through complex modelling, and [PERSON] et al. conducted a series of studies on truck driving safety, for example, simulation-based single-vehicle accident evaluation models where extreme conditions, such as wind and snow are taken into account to predict the potential crash and injury risk of vehicles [19], a single vehicle safety index is introduced into the model to provide a reasonable assessment of accident risk by taking into account the uncertainty of key variables [20], after that, the driving safety of the truck platoon was considered and a safe driving model for the trucks platoon was developed [21]. The safety evaluation models already available have some reference significance for the analysis of truck-driving safety under crosswind conditions.