# UAV-Assisted Hybrid Scheme for Urban Road Safety Based on VANETs
## 3 UAV Assisted (UAVa) Reactive Protocol Strategy
### UAVa's Design Approach
#### 3.2.2 Route Discover Metrics
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **IBZ1** & **IAZ1** & **ICZ1** & **IAY1** & **IBY1** & **ICY1** & **ICX1** & **IAX1** & **IBX1** \\ \hline v = 0 & 0 & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) \\ v = 1:IBZ1 & - & 2.5 & 5 & \(\infty\) & 7.5 & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) \\ v = 2:IAZ1 & - & - & 5 & 6 & 7.5 & \(\infty\) & \(\infty\) & \(\infty\) & \(\infty\) \\ v = 3:ICZ1 & - & - & - & 6 & 7.5 & 7.75 & \(\infty\) & \(\infty\) & \(\infty\) \\ v = 4:IAY1 & - & - & - & - & 7.5 & 7.75 & \(\infty\) & 11 & 13 \\ v = 5:IBY1 & - & - & - & - & - & 7.75 & \(\infty\) & 11 & 13 \\ v = 6:ICY1 & - & - & - & - & - & - & 9.5 & 11 & 13 \\ v = 7:ICX1 & - & - & - & - & - & - & - & 11 & 11.5 \\ v = 8:IAX1 & - & - & - & - & - & - & - & - & 11.5 \\ w & 0 & 2.5 & 5 & 6 & 7.5 & 7.75 & 9.5 & 11 & 11.5 \\ \hline \end{tabular}
\end{table} 
Table 1: Calculating process. Assumption: For each intersection v, when traveling only through the visited intersection, source to v, distance (v) is the shortest route; if the source to v route does not exist, it is infinite (\(\infty\)). (Note: We do not assume that distance (v) is the actual shortest route for an unknown intersection.) The basic situation is that there is only one visited intersection, the first intersection, in this case, the assumption is negligible. Otherwise, assume the assumption of n-1 access intersections. For example, we select (v, u) as an edge, where u has the minimum distance (u) of any undefined intersection, and the edge (v, u) makes distance (u) = distance (v) + length (v, u). The distance (u) is considered to be the shortest route from the source to u, because if there is a shorter route, and if w is the first undefined intersection on the route, then according to the original assumption, the distance (w) > distance (u) causes incompatibility. Similarly, if there is a shorter route to u without using an undefined intersection, and if the last intersection on that route is w, then we will get distance (u) = distance (w) + length (w, u), also incompatible. After processing with u, it will still be true that for each undefined intersection w, distance (w) will be the shortest route from the source to w using the visited intersection. If there is a short path that does not go through u, we have already found it, and if there is a short path using u, we will update it during u processing. After the intersection is visited, the shortest route from source to any intersection v consists only of the visited intersection. Therefore distance (v) is the shortest route. Balanced to Avoid Potential Congestion: In our model, we are using a simple trick to regulate congestion before it occurs, by previous perception data we can say the maximum probability of congestion period is in the morning and in the afternoon. Basically, on holidays, during this time, the control room takes appropriate action by using UAVs to regulate congestion. We consider our RSUs maximum capacity of fifty nodes at a time in an intersection. If more than fifty nodes at a time appear is an intersection, then the RSU cannot control it. Packet loss will be started before starting  
Figure 3: Shortest route discovery metric. this predicament. The control room will take action and quickly launch UAVs to increase the RSUs' coverage and regulate potential congestion in this intersection.