# Risk Causal Analysis of Traffic-Intensive Waters Based on Infectious Disease Dynamics
## 3 Empirical Case Analysis
### Screening of Key Risk Factors of Ship Navigation  
#### 3.1.1 Data Collection of Navigation System Risk Factor  
The data of risk factors of ship navigation at the Yangtze River estuary were collected for case study. Some of the factors need to be statistically analyzed by questionnaires. Visibility and tide can be characterized by the number of days of poor visibility in the month and the number of tidal waves in the month. The number of days when the Beaufort wind scale is greater than 6, the number of days of poor visibility, and the number of large tides can be obtained by the meteorological data form China Meteorological Administration at the Yangtze River estuary and the actual observation data from Shanghai Pilot Station. The data of the tide data can be obtained from the tidal station of the Shanghai Pilot Station. The large tidal range is defined as the tidal range greater than or equal to 275 cm. The number of days that the Beaufort wind scale is greater than 6, the number of days of poor visibility, and the number of the large tidal range in 2017 are shown in Table 2.  
As can be seen in Table 1, the number of days of poor visibility per month, days that the Beaufort wind scale is greater than 6, and large tidal range is 15 days, 137 days, and 363 times, respectively. The corresponding risk occurrence probability \(P\) can be calculated as 0.041, 0.3753, and 0.5893, respectively.  
According to the accident statistics of the Shanghai Maritime Safety Administration (obtained from [[https://www.sh.msa.gov.cn/](https://www.sh.msa.gov.cn/)]([https://www.sh.msa.gov.cn/](https://www.sh.msa.gov.cn/))), the number of waterborne traffic accidents in level of general and above was 32, 32, 20, 14, 14, and 14 times from 2012 to 2017, respectively. After analyzing the specific causes of traffic accident above grade 1 (obtained from the accident report of the maritime administration department), the risk occurrence probability of each risk factor was obtained, as shown in Table 3.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Month** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** & **12** \\ \hline
**Poor visibility days** & 2 & 0 & 0 & 5 & 3 & 0 & 1 & 1 & 1 & 1 & 4 & 0 \\
**Beaufort wind scale** & 14 & 13 & 11 & 12 & 11 & 6 & 10 & 20 & 10 & 11 & 11 & 8 \\
**is greater than 6** & 31 & 28 & 30 & 30 & 31 & 30 & 31 & 30 & 31 & 30 & 31 \\
**Number of large** & 31 & 28 & 30 & 30 & 31 & 30 & 31 & 30 & 30 & 31 & 30 & 31 \\
**tidal range** & & & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: The number of days of poor visibility, that when the Beaufort wind scale is greater than 6, and that of the large tidal range in each month of 2017.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type of Risk Factors** & **Risk Factors** & **Quantity** & **Frequency** \\ \hline  & Wave level & 30 & 0.2678 \\  & Flow state & 25 & 0.2232 \\  & Traffic flow density & 75 & 0.6696 \\ Environment & Flow & 33 & 0.2946 \\  & Channel water depth & 3 & 0.0268 \\  & Speed & 3 & 0.0268 \\  & Route complexity & 3 & 0.0268 \\  & Ship front and rear spacing & 5 & 0.0446 \\ \hline \hline \multirow{3}{*}{Management} & Navigation regulation rationality & 35 & 0.3125 \\  & VTS (vessel traffic service) & 2 & 0.0179 \\  & coordination degree & 2 & 0.0893 \\ \hline \multirow{3}{*}{Human} & \multicolumn{3}{c}{Onboard officer duties} & 50 \\  & Onboard officer skill & 51 & 0.4554 \\ \hline \multirow{2}{*}{Ship} & \multicolumn{3}{c}{Ship age} & 15 \\  & Ship navigation performance & 21 & 0.1875 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Statistics of risk factors at the Yangtze River estuary from 2012 to 2017.