# An Intersection Signal Control Mechanism Assisted by Vehicular Ad Hoc Networks
## 4 Simulation and Analysis
### Simulation Environment and Parameter Settings  
First, we constructed a typical intersection environment (as shown in Figure 1), which was formed by four bidirectional six-lane roads with a length of 1 km and an intersection with one left-turn lane and two straight lanes in each entrance direction. The upper bound (\(\overline{T_{g}}\)) and lower bound (\(T_{g}\)) of green light duration were set to 20 s and 40 s, respectively; the yellow light duration (\(T_{y}\)) was set to 3s; and the intersection velocity limit (\(v_{s}\)) was 50 km/h. Second, using the OMNeT++ interface, five static network nodes were set up as RSUs at the center of the intersection and the other ends of the four roads. The RSUs could communicate directly with each other and moreover use the 802.11p standard protocol to send ICPs to each adjacent RSU every 2 s in order to collect the information of vehicles on the four roads, where the transmission range of one hop was set to 250 m. Furthermore, the vehicles were generated at the other end of each road toward the intersection, where the lengths of them were set to 5 m uniformly, the safe stopping distance was 2.5 m, and the velocities (km/h) were randomly generated according to a normal distribution N(50,100). According to the intersection environment above and multiple experiments, we adopted 30 veh/min (i.e., 30 vehicles per minute) as the maximum passing capacity of a single lane (\(\overline{k_{s}}\)) in the intersection.  
In order to evaluate the proposed mechanism thoroughly, in the simulation, three traffic flow environments were provided: (1) The same even traffic flows, which meant all traffic flows had the same average value and their generating time intervals followed the exponential distribution. (2) The same uneven traffic flows, which meant the average traffic flows over a relatively long period were same; however, in order to simulate the actual traffic condition with the signalized intersection, the smooth flows above were separated into several sections according to their different entered flows, i.e., going straight (larger than others), turning left, and turning right. (3) Different traffic flows, for which we selected and set the values of the north-to-south and north-to-east flows to be twice as large as the others to observe the efficiency of the signal control mechanism in the case of differences in traffic flows. The standard value of the traffic flow was set to 150/200/250/300/350 veh/lane/h in five types of simulation tests and each one was run ten times with different random seeds to generate vehicles.  
For comparing the performances of our two implementation schemes based on the proposed mechanism assisted by far vehicle information, i.e., the fixed phase and period signal timing improvement scheme (fixed-FA), and the dynamic phase and period signal control scheme (dynamic-FA), the traditional signal timing scheme (traditional timing) that made the decision only considered the intersection vehicles was executed as well. The duration of the simulation was 1800 s. From the simulation results, we adopted the average waiting time of vehicles and the ratio of long-waiting vehicles (waits exceeding 120 s) as evaluation indices to analyze the performance. In addition, in the dynamic-FA, the adjustment factor \(\alpha\) for \(T_{d}^{\prime}\) was set to 0.049, which could reach three times the weight for a waiting time of 120 s.