## 4 Empirical Study and Result
### Analysis of Merging Behavior in Different Work Zones Layouts
#### 4.3.3 Speed and Speed Impact Differences  
The most crucial difference between Sites A3 and B4 is the speed distribution and the impact on surrounding vehicles. Table 3 displays the descriptive statistics of the speed of each lane in the direction. The mean velocities of the merge lane at Sites A3 and A4 are 78.28 km/h and 77.75 km/h, which are 11.36% and 11.96% lower than Site B4. As the speed distributions in Table 2 show, the average speed in the outside lane will be the lowest in all three lanes. However, at Site A3, the slowest lane is the middle lane, under a similar density range to Site B4. And the average speed in the through lane is 20.87% lower than in the merge lane. According to vehicle trajectories in Figure 4e,f and the results in Table 3, the layout of the solid white lines is responsible for the traffic oscillation and speed reduction at Site A3. Figure 9: Gap distribution of Scenario 2 and Scenario 3. Sites A3 and B4 exhibit more defined peaks, while Site A4 has a more uniform distribution, likely due to its smaller sample size and lower traffic volume. During the merging process, the speed series of the target follower of the merging vehicle is extracted. Three parameters involved in the follower's speed change are counted in Table 4. \"Delta\" denotes the difference in the follower's speed between the end and the beginning of the series. \"Std\" represents the standard deviation of the speed series. And \"Range\" means the difference between the maximum and the minimum of the value in the series. The change in the follower's speed reflects the merging impact on the surrounding vehicles. In this study, the negative effect on the follower in the open lane is the largest on a two-lane highway. At Sites A3 and A4, the merging vehicle can result in the most \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **Lane** & **Count** & **Mean** & **std** & **min** & **25\%** & **Median** & **75\%** & **max** \\ \hline \multirow{3}{*}{A3} & Merge & & 78.28 & 11.85 & 20.80 & 71.59 & 79.31 & 86.32 & 115.14 \\  & Through & 3670 & 61.94 & 12.96 & 21.69 & 53.26 & 63.08 & 71.76 & 93.95 \\  & Outer & & 65.31 & 10.39 & 32.86 & 58.13 & 64.75 & 72.04 & 108.49 \\ \hline \multirow{3}{*}{B4} & Merge & & 88.31 & 7.44 & 50.50 & 84.20 & 88.66 & 92.87 & 116.81 \\  & Through & 2722 & 80.40 & 7.43 & 42.48 & 76.06 & 80.85 & 85.26 & 108.79 \\  & Outer & & 73.39 & 7.68 & 40.20 & 68.32 & 73.06 & 78.29 & 101.92 \\ \hline \multirow{3}{*}{A4} & Merge & & 77.75 & 8.66 & 52.19 & 72.05 & 77.71 & 84.00 & 107.68 \\  & Through & 973 & 67.89 & 10.98 & 24.49 & 64.65 & 70.26 & 74.32 & 92.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Descriptive statistics of lane speed distribution at Sites A3, B4, and A4. Figure 10: Scatter plot of start speed and gap. Higher start speeds generally correspond with larger gaps at Site A3, while at Site A4, gap selection is less influenced by start speed. considerable deceleration of its target follower by about 65 km/h, and oscillations or accidents are more likely to occur in Scenarios 2 and 3. The relationship between the finishing speed of the merging vehicle and the impact on followers' speed decrease is shown in Figure 11. The distributions at Sites A3 and B4 are similar, but at Site A3, with density increases, the merging vehicle would lead to a more significant speed reduction and lower finishing speed. The relationship at Site A4 is approximately linearly distributed, which means that the impact on the target follower is more deterministic than in a three-lane highway work zone. Overall, the speed distribution and its impact on surrounding vehicles, as shown in Table 3, reveal notable differences between Sites A3 and B4. At Site A3, the speed reduction in the outer lane is more pronounced, likely due to the influence of the solid white lines, which restrict lane changes and cause traffic oscillations.