# An Intersection Signal Control Mechanism Assisted by Vehicular Ad Hoc Networks
## 2 Information Collection for Far Vehicles  
So far, in most of the scientific research and engineering applications, the traffic signal control system at the urban intersection generally collects the information of vehicles within the intersection area as the input data for modeling and calculation. The data can be easily acquired and then preliminarily analyzed using visual sensor devices at the intersection (e.g., cameras) and some corresponding image processing techniques. However, vehicles that have not entered the intersection area before the decision-making time may reach the intersection later, potentially impacting the effectiveness and accuracy of the decision. As shown in Figure 1, at time \(t_{1}\), based on the information of vehicles within the intersection area, the signal control system makes the decision to change to a green light for the north-south bidirectional traffic flows. At a later time \(t_{2}\), a large number of vehicles on the east side enter the intersection area and encounter the forbidden signal. They have to wait for the right-of-way, which results in an increase in overall delay time and a decline in traffic capacity at the intersection. Therefore, it is clear that the information of the vehicles in the non-intersection area (which we call far vehicles in this paper) is of great significance for the signal control decision. In this paper, a VANET was used to collect the real-time information of the far vehicles on the road. The assumptions and method were as follows. It was assumed that all vehicles are equipped with the on-board equipment supporting V2V and V2I communication. The roadside unit (RSU) that can communicate with vehicles is deployed at each intersection to collect and process the real-time information of vehicles, and then provide them to the signal control system for decision-making; each RSU can directly communicate and exchange data with its adjacent RSUs through wired or cellular networks. \begin{table}
\begin{tabular}{c c} \hline \hline
**Notation** & **Description** \\ \hline \(t_{c}\) & Current moment \\ \(t_{f}\) & Future moment \\ \(n_{max}\) & Capacity of the road \\ \(n_{id}\) & Number of vehicles in the “island” \\ \(v^{t_{c}}\) & Real-time velocities at \(t_{c}\) \\ \(pos^{t_{c}}\) & Real-time positions at \(t_{c}\) \\ \(T_{ls}\) & The time that the vehicle has been waiting for \\ \(T_{d}^{j}\) & Estimated waiting time of vehicle \(j\) \\ \(WT_{i}\) & Estimated waiting time of traffic flow \(i\) \\ \(P_{i}\) & \(i\)th signal phase \\ \(qt_{i}^{t_{f}}\) & Number of vehicles in flow \(i\) that have stopped at \(t_{f}\) \\ \(k_{i}^{T_{g}}\) & The vehicles in the \(i\)th traffic flow that can pass the \\ \(T_{d}^{\prime}\) & Intersection in \(T_{g}\) \\ \(ET_{P_{i}}^{f-t_{c}}\) & Adjusted waiting time \\ \(ET_{P_{j}}^{f-t_{c}}\) & The eliminable waiting time of the phase \(P_{i}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of presented symbols. For vehicle information collection, we assumed that each vehicle is equipped with the Global Position System (GPS) and the digital map, and then it can easily acquire the information about its own position, velocity, moving direction, etc. With the aid of the periodical beacon messages (which are mandatory in most of VANETs protocols, e.g., 802.11p), which are exchanged with each other, and the information can also be obtained by their neighboring vehicles within the transmission range. Each RSU sends a dedicated packet, i.e., an ICP (information collection packet), to each adjacent intersection through a VANET at fixed time intervals. The ICP is relayed using a multi-hop connection through all vehicle nodes on the road sequentially. After any vehicle-node receives it, it attaches its information including its own ID, current velocity (\(v\)), current position (\(pos\)), acceleration (\(acc\)), deceleration (\(dec\)), desired velocity (\(v_{d}\)), and vehicle length (\(clen\)) to the packet.