## 4 Scenario Analysis
### Preparation of Scenarios  
Four main scenarios and eight sub-scenarios were constructed for the simulations to evaluate the applicability of RM in the study. Each scenario was modeled based on the calibrated VISSIM network and evaluated independently from the others. Base scenario (current condition, BS)--the initially calibrated model is simulated without RM application. The results from this scenario serve as a reference for all other scenarios to evaluate the effectiveness of RM implementation. Alternative scenario 1 (on-ramp closure, AS-1)--although an RM signal is provided, it will be red during the simulation period. Therefore, vehicles from the adjacent roads are not allowed to merge into the freeway. This situation seems illogical, but this assumption is necessary to calculate the maximum values of the freeway speed. Alternative scenario 2 (off-ramp closure, AS-2)--since the off-ramp is closed in this scenario, vehicles on the freeway cannot use it to exit. Therefore, this scenario can reveal the effect of weaving around the area. If this scenario can return positive results, then this can also be considered a temporary solution to traffic congestion during peak hours. Alternative scenario 3 (fixed time RM, AS-3)--the signal on the ramp operates with minimum red time, following a metering rate prescribed for the particular control period. This pre-timed operation is known as the simplest and least expensive form of RM for construction and installation, as well as the most rigid approach [8]. In this scenario, the red signal will always be active unless at least one vehicle is detected upstream of the signal. The signal has two detection loops, as shown in Figure 4: the first detector (presence detector) senses vehicle access to the signal and the second detector (counting detector) counts the number of vehicles that pass the signal. Under this scenario, eight sub-scenarios were designed by changing the number of vehicles that the RM signal can serve during the green time and the minimum red time, as shown in Table 3, to find the most recommended combination of them. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Default**} & \multicolumn{2}{c}{**Suggested**} & \multicolumn{2}{c}{**Calibrated Value**} \\ \cline{2-7}  & **Own** & **Trailing** & **Own** & **Trailing** & **Own** & **Trailing** \\ \hline Maximum deceleration (m/s\({}^{2}\)) & \(-4\) & \(-3\) & \((-4.6)\)–\((-3.7)\) & \((-3.7)\)–\((-2.4)\) & \(-4.6\) & \(-3.7\) \\ \hline Accepted deceleration (m/s\({}^{2}\)) & \(-1\) & \(-0.5\) & \((-0.8)\)–\((-1.2)\) & \((-0.5)\)–\((-0.8)\) & \(-1\) & \(-0.5\) \\ \hline \(-1\) m/s\({}^{2}\) per distance (m) & 61 & 61 & 45.7–76.2 & 61 & \\ \hline Waiting time before diffusion (s) & 60 & 200 & 200 & 200 & \\ \hline Min. headway (front/rear) (m) & 0.5 & 0.46–0.61 & 0.46 & \\ \hline To slower lane if collision time above (s) & 0 & 0-0.5 & 0 & \\ \hline Safety distance reduction factor & 0.6 & 0.25–1 & 0.25 & \\ \hline Maximum deceleration for cooperative & \(-3\) & \((-2.4)\)–\((-4.6)\) & \(-4.6\) & \\ \hline Overtake reduced speed areas & No & No & No & No \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Selected values for the parameters of the necessary lane-change model. Alternative scenario 4 (traffic responsive RM, AS-4)--the traffic condition of the freeway directly influences the metering rate the ramp in this traffic responsive RM. Although there are more costs, such as freeway loop detectors or other surveillance systems, this alternative is more easily adoptable to change current conditions. Furthermore, this is known to provide better results than the pre-timed options [8]. This research uses three detectors. The first detector (occupancy detector) is located on the freeway downstream of the merging area to calculate the occupancy rate in the mainline. The second detector (presence detector) is located right before the signal to sense vehicle approach.