## 3 Construction of a Risk Evaluation Model for Hazardous Chemical Road Transportation Accidents
### Cloud Model Evaluation Method
#### 3.2.2 Construction of Cloud Models  
A comprehensive risk cloud for hazardous chemical road transport accidents is constructed with the following steps [25]. (1) Determine the risk level standard cloud. The evaluation of the indicators of the cloud model is expressed as the concept of expressing the fuzzy good and bad of things, and the comment of the evaluation indicators in each comprehensive evaluation system has different characteristics according to the evaluator, so the determination of the standard cloud of the cloud model is an important prerequisite for the subsequent risk cloud and comprehensive cloud of the cloud model. Considering the reality of road transport of dangerous chemicals and the suggestions of experts from various parties, combined with the habit of the language expression of road transport accidents of dangerous chemicals, the risk evaluation level of hazardous chemical road transport accidents is divided into 5 levels: \"very low risk\", \"low risk\", \"medium risk\", \"high risk\", and \"very high risk\". The numerical features of each level are transformed into standard clouds by using the forward cloud generator of the cloud model. The cloud parameters for each level interval \([x_{\text{min}},x_{\text{max}}]\) are calculated as follows [26]. \[\left\{ \begin{array}{l}E_{x_{0}}=\frac{x_{\text{max}}+x_{\text{min}}}{2}\\ E_{n_{0}}=\frac{x_{\text{max}}-x_{\text{min}}}{6}\\ H_{e_{0}}=k\end{array} \right. \tag{13}\]  
where k is the super entropy value, reflecting the cohesiveness of the cloud droplets. The smaller its value is, the smaller the dispersion of the cloud droplets and the thinner the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Digital Characteristic** & **Meaning** & **Formula** \\ \hline \multirow{4}{*}{\(E_{x}\)} & The point in the space of the argument domain that reflects the qualitative concept is the cloud center of gravity of the cloud droplet group. The greater the expectation, the higher the risk level. & \(E_{x}=\overline{X}=\frac{1}{n}\sum\limits_{i=1}^{n}x_{i}\) \\ \hline \multirow{4}{*}{\(E_{n}\)} & Uncertainty measures of qualitative concepts, determined by the fuzziness and probability of the metric qualitative concepts, can reflect the degree of discrete cloud droplets. The greater the entropy value, the greater the ambiguity, and the lower the credibility of the evaluation results. & \(E_{n}=\sqrt{\frac{\pi}{2}}\times\frac{1}{n}\sum\limits_{i=1}^{n}\left|x_{i}- \overline{X}\right|\) \\  & the greater the ambiguity, and the lower the credibility of the evaluation results. & \\ \hline \multirow{4}{*}{\(H_{e}\)} & An uncertain measure of entropy that reflects the degree of cohesion of the cloud droplets. The greater the hyperentropy, the thicker the cloud layer, the greater the randomness, and the lower the stability value. & \(H_{e}=\sqrt{|S^{2}-E_{n}^{2}|}\) \\ \cline{1-1}  & the randomness, and the lower the stability value. & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Numerical Characterization of Cloud Models. normal cloud [27]. k is the constant, which can be adjusted based on the uncertainty and randomness of the specific index. It is generally taken as 0.1. The numerical characteristics of the standard cloud can be obtained based on the equation above, as shown in Table 3.  
(2) Calculate the risk cloud of the evaluation indicators. The raw data are obtained by distributing questionnaires to experts and scoring the risk level. The raw data were input into the backward cloud generator and calculated using the following formula to determine the risk cloud of hazardous chemical road transportation accident evaluation indicators. \[\left\{ \begin{array}{l}E_{xj}=\overline{X}=\frac{1}{n}\sum\limits_{i=1}^{n}x_ {ij}\\ E_{nj}=\sqrt{\frac{\pi}{2}}\times\frac{1}{n}\sum\limits_{i=1}^{n}|x_{ij}- \overline{X}|\\ H_{ej}=\sqrt{\left|S_{j}^{2}-E_{nj}^{2}\right|}\\ S_{j}^{2}=\frac{1}{n-1}\sum\limits_{i=1}^{n}\left(x_{ij}-\overline{X}\right)^{2 }\end{array} \right.