## 3 Proposed Yielding Protocol
### Decision on Yielding  
A vehicle that has received a yielding request decides whether to yield the way based on its speed, moving direction, and information about the surroundings captured by its sensors. The criteria used to make this decision depend on the particular yielding pattern. The former method considered several criteria, such as whether there is a traffic light, whether the vehicle can stop safely, how the vehicle ahead behaves, how many low-priority vehicles are queuing up, and whether there is a vehicle in the back. To enhance yielding efficiency, this paper additionally considers whether there is a conflict situation, whether there are pedestrians wanting to cross a road, whether there is enough space to move into, and what is the priority level of the road the own vehicle is running, as shown in Figure 4. Here, the space to move into means space on the target lane that the low-priority vehicle will move into when the responding vehicle has yielded the way. The driver in a human-driven vehicle sends an  
Figure 3: Determining the relative direction of the communicating vehicle. The red vehicle is the own vehicle. agreement message through a UI, as shown in Figure 1, but does not send an agreement message if there is no conflict situation. If only one lane intersects with the course of the own vehicle as in Patterns 1 and 4 (the lane going left to which the own vehicle wants to turn in Pattern 1; the opposite lane that the own vehicle will cross when it turns right in Pattern 4), the yielding decision is made based on whether there is a traffic light, whether there is a conflict situation, whether the vehicle can stop safely, how the vehicle beyond the intersection behaves, how many low-priority vehicles are queuing up, whether there is a vehicle in the back, and whether there are pedestrians, as shown in Figure 4a. If two lanes intersect with the course of the own vehicle as in Patterns 2 and 3 (the lane going left and the lane going right to which the own vehicle wants to turn in Pattern 2, or the two lanes that the own vehicle needs to cross in Pattern 3), the yielding decision is made based on whether there is a traffic light, whether there is a conflict situation, whether the vehicle can stop safely, whether there is enough space to move into for the vehicle on the opposite lane, how the vehicle beyond the intersection behaves, how many low-priority vehicles are queuing up, whether there is a vehicle in the back, and whether there are pedestrians, as shown in Figure 4b. Figure 4: Yielding decision flow. TL: Traffic light; CS: Conflict situation; SS: Stop safely; RP: Road priority; VI: Vehicle beyond the intersection; VB: Vehicle in the back; NO: Number of queuing vehicles; PS: Pedestrians in the surroundings; AS: Availability of enough space. (**a**) Patterns 1 and 4; (**b**) patterns 2 and 3. The general idea of the above decision flows is first to decide whether the situation warrants yielding, second to decide whether yielding can be done safely, and third to decide whether yielding improves traffic efficiency. The decision on whether the situation warrants yielding is based on the first two criteria: Whether there is a traffic light and whether there is a conflict situation. If there is no conflict situation, the responding vehicle does not need to control its speed. It yields the way but does not slow down or stop. However, if there is a vehicle in the back, that vehicle may encounter a conflict situation. In such a case, the vehicle that has received a yielding request does not respond but leaves the yielding decision to the vehicle in the back. The decision on whether yielding can be done safely is based on whether the vehicle can stop safely. The vehicle can stop safely if the following is satisfied:  
\[v\left(-\frac{v}{dec}+RT\right)+\frac{v^{2}}{2 dec}<d_{I} \tag{1}\]  
Where \(v\) is the current speed, \(dec\) is the permitted maximum rate of deceleration, \(RT\) is the driver's response time, and \(d_{I}\) is the estimated distance to the intersection.