# Optimization Strategy for Electric Vehicle Routing under Traffic Impedance Guidance
## 5 Case Analysis
### Analysis of the Impacts on the Transportation Side  
When EVs trigger the charging demand during the driving process, they will travel to the corresponding charging station along the optimal path based on the current location and the corresponding scenario. According to the study in reference [33], when a large number of EVs concentrate on charging, it will have an impact on the surrounding traffic conditions and exacerbate congestion near the charging stations. The number of vehicles accessing the charging station at different times of the day is shown in Figure 16a,b. Looking at the two scenarios combined, EVs in both scenarios tend to gather at the charging stations during the morning and evening peak periods. In the morning, a large proportion of EVs with work-related demands drive to the work area and trigger the charging demand. EVs with entertainment demands and some work-related demands enter the commercial area for charging while charging stations in residential areas are more frequented by EVs driving within residential areas for daily-life demands. In the  
Figure 16: Number of EVs in (**a**) unguided scenario and (**b**) time-guided scenario. Figure 15: Voltage levels at different nodes under varying EV penetration rates. evening, as all EVs return to residential areas, charging vehicles are concentrated mostly in residential areas. In the unguided scenario, as shown in Figure 16a, there is a significant difference in the number of vehicles entering each charging station, and the distribution is uneven. During the morning peak period, most of the charging vehicles are concentrated at stations 1 and 3, while during the evening peak period, they are mostly concentrated at station 5. This is because in the unguided paths, distance is prioritized, and charging stations located closer to the central areas of each region are chosen first to shorten the travel distance. This may lead to increased traffic congestion around the charging stations. Comparing the unguided scenario with the time-guided scenario, as shown in Figure 16b, it can be seen that, especially during the morning peak period, the distribution of charging vehicles is more balanced. Due to the higher congestion levels in the central areas of each region, especially in the commercial area, the vehicles that were originally charging at stations 1 and 3 are guided to stations 2, 4, and 5, located near the smooth traffic sections. During the evening peak period, all private vehicles return to residential areas, and in the time-guided scenario, EVs still gather in residential areas for charging. However, compared to before, some EVs that were originally concentrated at station 5 are guided to station 4. The number of charging vehicles in residential areas is clearly shared between stations 4 and 5, alleviating the extra congestion caused by excessive concentration of EVs at a single charging station. In other words, in the time-guided scenario, while saving user's time costs, the distribution of vehicles between charging stations is balanced, and traffic congestion is alleviated. To quantify the alleviation of traffic congestion by EV route planning in the time-guided scenario, we can refer to Figure 17. We selected 9 am during the peak period and combined it with real-time congestion information of the roads around each charging station to obtain the average road impedance. The heat columns on the charging station nodes represent the average road impedance around them. The left side represents the unguided scenario, while the right side represents the time-guided scenario. By comparing the two, we can observe that the time-guided scenario, guided by the shortest travel time, changes the charging time period for EVs, avoiding concentrated charging during peak hours. This significantly reduces the travel time on the roads near the charging stations, thereby alleviating the level of traffic congestion. As the penetration rate of EVs increases, the road impedance around charging stations also changes.