*3.2. Analysis of Various Tra*ffi*c Signal Coordination Plans*

The effects of various signal coordination plans on BEV and ICEV energy/fuel consumption were also investigated. A previous study found that good traffic signal coordination can significantly reduce fuel consumption and ICEV emissions [14]. Figure 6 illustrates a sample corridor with three intersections and four links. Each link was 0.5 km in length which is a reasonable intersection length in an urban area. The demand from the start node to the end node was 1200 veh/h. The last vehicle injected into the simulation departed 15 min from the beginning of the simulation. A free speed of 80 km/h was applied to the entire corridor. This scenario was meant to show how a signal coordination plan can affect the energy/fuel consumption in a specific corridor. To evaluate the effects of signal coordination in this study, three scenarios were adopted: (1) a poorly coordinated fixed-time signal plan, (2) a partially coordinated fixed-time signal plan, and (3) a well-coordinated fixed-time signal plan. Each traffic signal had a 60 s cycle length, 30 s effective green time, and a 2.5 s effective lost time.

**Figure 6.** A sample coordinated corridor.

Figure 7 illustrates the effects of different signal coordination plans on BEV and ICEV energy/fuel consumption and vehicle delay. As expected, the well-coordinated signal plan significantly reduced vehicle delay from 72.64 s to 15.51 s compared to the poorly coordinated signal plan. The well-coordinated signal plan also reduced vehicle delay by 26% compared to the partially coordinated signal plan. Figure 7 also shows that the well-coordinated signal plan improved energy/fuel efficiency in both ICEVs and BEVs. In particular, ICEVs' fuel consumption was reduced by 28% and 35% compared to the partially coordinated and poorly coordinated signal plans, respectively, while BEVs' energy efficiency was improved by 17% and 20%, respectively. These results indicate that BEVs' energy consumption was less sensitive to signal coordination than ICEVs' fuel consumption, since BEVs produced more regenerative energy on the corridors with partially and poorly coordinated signal plans. The BEVs recovered 21%, 40%, and 49% of total energy through regenerative braking for the well-coordinated, partially coordinated, and poorly coordinated signal plans, respectively, as illustrated in Figure 8.

**Figure 7.** BEV and ICEV energy/fuel consumption for different signal coordination plans.

**Figure 8.** Regenerated energy of BEV for different signal coordination plans.

### **4. Conclusions and Recommendations for Future Research**

This study investigated the effects of different intersection controls (i.e., a roundabout, traffic signal, and stop sign) and signal coordination plans (i.e., well-coordinated, partially coordinated, and poorly coordinated) on BEV and ICEV energy/fuel consumption. The second-by-second speed profiles of individual vehicles were derived from a traffic simulation model, and the speed profiles were utilized as inputs to estimate ICEV fuel consumption and BEV energy consumption using microscopic fuel consumption and energy models.

The results indicate that the most energy/fuel efficient traffic controls are different for BEVs and ICEVs. For BEVs approaching an intersection at a speed of 88 km/h, the roundabout was the most energy-efficient intersection control, while the stop sign was the least energy efficient. In contrast, for ICEVs at the same approach speed, the two-way stop sign was the most fuel-efficient control, while the roundabout was the least fuel efficient. The BEV and ICEV energy/fuel consumption patterns also differed at other approach speeds (72 and 56 km/h). For BEVs, the energy consumption at all intersection control types was similar, while for ICEVs, stop-sign-controlled intersections significantly reduced fuel consumption compared to the other two intersection types.

The ICEVs' higher fuel consumption levels at roundabouts resulted from acceleration leaving the roundabout, as acceleration rate is a major contributor to vehicle fuel consumption. The BEVs' energy consumption levels were less affected by the intersection control strategy than were ICEVs'. This can be attributed to the energy regenerated by BEVs during deceleration; BEVs recovered 32.9% of the total energy through regenerative braking at the roundabout for an approach speed of 88 km/h, thereby improving overall energy efficiency.

The effects of different signal coordination plans on energy/fuel consumption were also investigated for BEVs and ICEVs. Both BEV and ICEV energy/fuel efficiency was improved by the well-coordinated signal plan. Signal coordination had a weaker effect on energy efficiency in BEVs compared to ICEVs, because BEVs produced more regenerative energy on corridors with partially and poorly coordinated signal plans. The study found BEVs recovered 21%, 40%, and 49% of total energy through regenerative braking on the corridors for well-coordinated, partially coordinated, and poorly coordinated signal plans, respectively.

In summary, this study demonstrated that regenerative energy in BEVs is a critical factor in energy efficiency. Among the tested intersection controls, BEVs recovered the largest amount of energy at the roundabout for the studied intersection site. The market penetration rate of BEVs has increased sharply in recent years, and the number of BEVs on the road is expected to continue to increase in the near future. Recently, a number of transportation researchers and engineers have developed fuel-efficient

transportation facilities and control strategies to improve fuel economy and reduce ICEV emissions. The findings of this study suggest that transportation facilities and control strategies should be designed to enhance BEVs' energy efficiency, particularly in zero-emission zones [23], where only BEVs can be utilized. Furthermore, the findings of this study can be used in the development of energy-efficient routing strategies. For example, the routing of BEVs might entail sending the vehicles through roundabouts, whereas the routing for ICEVs might send the vehicles through two-way stop sign intersections.

Future research will investigate the effects of combinations of various vehicle types, different demand levels, and more facility types on BEVs' energy consumption. The development of a multimodal traffic signal control system that can improve both BEV and ICEV energy/fuel efficiencies is also recommended.

**Author Contributions:** The authors confirm contributions to the paper as follows: study conception and design, K.A., S.P.; simulation model development, K.A., S.P.; analysis and interpretation of results, K.A., H.A.R.; draft manuscript preparation, K.A., H.A.R. All authors reviewed the results and approved the final version of the manuscript.

**Funding:** This work was funded by the Department of Energy through the Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office, Energy Efficient Mobility Systems Program under award number DE-EE0008209.

**Conflicts of Interest:** The authors declare no conflict of interest.
