## 3 Proposed Yielding Protocol
### Identification of the Communicating Vehicle  
The yielding process does not involve all the vehicles near the intersection but only two specific vehicles. The vehicle that requests yielding and the vehicle that responds and yields the way need to identify each other. However, it is not possible to pinpoint the position of a running vehicle, and the GPS information includes some error. Some vehicles may not communicate. Thus, the responding vehicle cannot be identified reliably by the position information alone. If a wrong vehicle is identified as the communicating vehicle, a dangerous situation may arise. To address this problem, the former method identified the communicating vehicle by recognizing the vehicle model from the video captured by the vehicle-mounted camera and based on the position information and vehicle information included in the received message. However, this approach has a problem in vehicle identification accuracy when there are several similar looking vehicles. The present method enhances the accuracy level of vehicle identification by narrowing down the vehicles to be detected by additionally calculating and using the vehicle direction. The vehicle identification algorithm used is described in Algorithm 1: \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Message Element** \\ \hline \multirow{3}{*}{**Header**} & Yielding message identifier \\  & Message length \\  & Yielding ID \\ \hline \multirow{6}{*}{Body} & \multirow{6}{*}{Sender vehicle information} \\  & & Vehicle color \\ \cline{1-1}  & & Longitude \\ \cline{1-1}  & & Latitude \\ \cline{1-1}  & & Angle of moving direction \\ \cline{1-1} \cline{2-3} \cline{3-3}  & & Yielding pattern number \\ \cline{1-1} \cline{2-3}  & & Message type \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Yielding message structure. Here, the relative position in Step 2 is the direction from the own vehicle. It represents the angle of direction in which the other vehicle is located, \(\theta\)pos, in the counterclockwise rotation with the direction in which the own vehicle is moving defined as \"0.\" It is calculated by converting the longitude and the latitude into plane rectangular coordinates. In the case where the own vehicle is the requesting vehicle, it is near the intersection. Therefore, as shown in Figure 2a, it determines that an approaching vehicle is on its left if the latter is located within the \(90^{\circ}\) of \(0\leq\theta\)pos \(\leq\pi\gamma 2\), in the back if it is located within the \(180^{\circ}\) of \(\pi\gamma 2<\theta\)pos \(\leq 3\pi\gamma 2\), on its right if it is located within the \(45^{\circ}\) of \(3\pi\gamma 2<\theta\)pos \(\leq 7\pi\gamma 4\), and ahead if it is located within the \(45^{\circ}\) of \(7\pi\gamma 4<\theta\)pos \(\leq 2\pi\). On the other hand, if the own vehicle is the responding vehicle, the requesting vehicle is near the intersection and the own vehicle may or may not be located near the intersection. Therefore, as shown in Figure 2b, it determines that a vehicle near the intersection is ahead if the latter is located within the \(120^{\circ}\) of \(0\leq\theta\)pos \(\leq\pi\gamma 3\) and \(5\pi\gamma 3<\theta\)pos \(\leq 2\pi\), on its left if it is located within the \(75^{\circ}\) of \(\pi\gamma 3<\theta\)pos \(\leq 3\pi\gamma 4\), in the back if is located within the \(90^{\circ}\) of \(3\pi\gamma 4<\theta\)pos \(\leq 5\pi\gamma 4\), and on its right if it is located within the \(75^{\circ}\) of \(5\pi\gamma 4<\theta\)pos \(\leq 5\pi\gamma 3\). The relative direction in Step 2 is the direction in which the other vehicle is moving as seen from the own vehicle.