## 4 Results and Descriptive Analysis
### Speed
#### 4.1.2 Influence of Median Opening Length on Speed  
Whether the vehicle running speeds of the work zones are consistent has a significant impact on the safety of traffic. When the speed difference between different areas is less than 10 km/h, the running speed coordination is good; when the speed difference is 10-20 km/h, the safety of traffic decreases with the increase in the speed difference; when the speed difference is greater than 20 km/h, the speed coordination is poor, leading to a high accident rate. Therefore, the speed difference should be kept within 10 km/h if the conditions allow [38]. As shown in Table 5, the speed difference between the running speeds of adjacent areas, the consistency of the running speed and speed limit and the analysis results of the influence of the opening length on speed under different opening lengths are reported. The U-test results indicated that there were significant differences in the average vehicle speed and running speed under different opening lengths at a 95% confidence level; the opening length had a significant positive correlation with the running speed when the width of the median and the cross slope were constant, and the longer the opening length, the slower the speed increased. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Area**} & \multirow{2}{*}{\begin{tabular}{c} **Maximum Speed** \\ **(km/h)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Minimum Speed** \\ **(km/h)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Running Speed/\(v_{85}\)** \\ **(km/h)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Mean Speed/\(v\)** \\ **(km/h)** \\ \end{tabular} } & \multirow{2}{*}{**SD**} & \multirow{2}{*}{
\begin{tabular}{c} **Speed Limit** \\ **Compliance Rate** \\ \end{tabular} } \\ \hline A (Car) & 104.39 & 68.13 & 101.53 & 90.96 & 10.78 & 16.67\% \\ A (Truck) & 95.80 & 51.06 & 88.52 & 72.85 & 13.10 & 70.83\% \\ A (All) & 104.39 & 51.06 & 98.23 & 81.90 & 15.03 & 43.75\% \\ B (Car) & 101.15 & 54.19 & 91.13 & 77.59 & 12.58 & 8.33\% \\ B (Truck) & 90.40 & 53.59 & 72.19 & 64.96 & 9.37 & 33.33\% \\ B (All) & 101.15 & 53.59 & 87.39 & 71.27 & 12.76 & 20.83\% \\ C (Car) & 90.68 & 49.61 & 74.44 & 64.69 & 10.44 & 41.67\% \\ C (Truck) & 78.15 & 48.44 & 61.06 & 56.64 & 6.92 & 75.00\% \\ C (All) & 90.68 & 48.44 & 70.98 & 60.66 & 9.73 & 58.33\% \\ D (Car) & 66.18 & 31.02 & 51.43 & 44.33 & 8.46 & 95.83\% \\ D (Truck) & 53.38 & 27.19 & 39.14 & 35.89 & 5.48 & 100.00\% \\ D (All) & 66.18 & 27.19 & 50.07 & 40.11 & 8.28 & 97.92\% \\ E (Car) & 74.47 & 41.17 & 62.52 & 56.87 & 7.10 & 66.67\% \\ E (Truck) & 64.60 & 36.88 & 56.97 & 50.06 & 7.21 & 95.83\% \\ E (All) & 74.47 & 36.88 & 61.06 & 53.47 & 7.92 & 81.25\% \\ F (Car) & 78.11 & 49.07 & 73.99 & 61.96 & 9.03 & 41.67\% \\ F (Truck) & 72.94 & 42.44 & 65.64 & 55.88 & 8.15 & 70.83\% \\ F (All) & 78.11 & 42.44 & 70.72 & 58.92 & 9.12 & 56.25\% \\ G (Car) & 86.42 & 43.94 & 80.30 & 67.15 & 12.91 & 37.50\% \\ G (Truck) & 73.82 & 49.34 & 65.18 & 59.05 & 6.84 & 54.17\% \\ G (All) & 86.42 & 43.94 & 76.34 & 63.12 & 11.09 & 45.83\% \\ H (Car) & 73.28 & 44.40 & 64.08 & 55.74 & 8.77 & 66.67\% \\ H (Truck) & 64.36 & 42.04 & 57.16 & 52.19 & 5.67 & 95.83\% \\ H (All) & 73.28 & 42.04 & 61.88 & 53.97 & 7.59 & 81.25\% \\ I (Car) & 53.53 & 32.74 & 49.48 & 44.73 & 5.16 & 100.00\% \\ I (Truck) & 53.25 & 32.82 & 44.52 & 40.12 & 5.38 & 100.00\% \\ I (All) & 53.53 & 32.74 & 48.14 & 42.42 & 5.75 & 100.00\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of vehicle speed statistics for different areas and vehicles. When the opening length was 40 m, the vehicle running speed was 50.07 km/h, which is inconsistent with the theoretical value calculated by the model (40 km/h) and the speed limit (60 km/h). Its speed difference with the upstream transition area was greater than 20 km/h, and that with the activity area was greater than 10 km/h. The speed dispersion was small, and the speed limit compliance rate was high. The speed coordination was poor, so there were safety hazards.