*3.2. Eco-CACC-I for ICEVs*

The Eco-CACC-I for ICEVs previously developed in [19,20] was considered in comparison with the Eco-CACC-I for BEVs. In this model, the optimization problem was formulated using Equations (2) through (4), and the same vehicle dynamic model used in Equations (5) through (7). Note that the Virginia Tech comprehensive power-based fuel consumption model (VT-CPFM-1) was used in place of the BEV energy model in Equations (8) through (11). More details of the Eco-CACC-I controller for ICEVs can be found in [19,20].

The same simulation was conducted for a 2015 Honda Fit, which has an engine power and weight similar to the 2015 Nissan Leaf. The test results are presented in Figures 4 and 5. Figure 4 shows the test results for a speed limit of 25 mph for different signal timings and roadway grades. All the images in the left column in Figure 4 demonstrate that the speed profile with a deceleration level in the middle area (between the minimum and maximum values) was the optimal solution for the uphill direction. All the images in the right column in Figure 4 demonstrate that the speed profile associated with the maximum deceleration level was the optimal solution for the downhill direction. The corresponding energy consumption levels for each feasible solution (speed profile) in the solution space are presented in Figure 5. Note that the solution index along the *x*-axis is also

ranked and ordered in a descending manner based on the deceleration level. The energy consumption unit is "liters" for ICEVs. In addition, unlike BEVs that regenerate energy while braking, ICEVs always consume fuel during the trip. All the images in the left column in Figure 5 show that the vehicle consumed more energy to reach a higher cruise speed in the uphill direction upstream of the intersection. However, higher cruise speeds resulted in less energy consumption downstream of the intersection. Therefore, the optimal solution for ICEVs driving in the uphill direction is somewhere in the mid-range, depending on the vehicle's specifications and roadway grade. All the images in the right column in Figure 5 demonstrated that different deceleration levels did not change the ICEV's energy consumption while traveling downhill. Therefore, higher cruise speeds resulted in the same level of fuel consumption upstream of the intersection. However, higher cruise speeds resulted in less energy consumption downstream of the intersection. In this case, the deceleration level is the most important factor in locating the optimal solution. Higher deceleration levels corresponded to lower energy consumption for the downstream portion, while energy consumption remained the same for the upstream portion. Therefore, the maximum deceleration level corresponds to the optimal solution for ICEVs driving in the downhill direction.

**Figure 4.** Honda Fit speed profile by ICEV Eco-CACC-I for a speed limit of 25 mph.

**Figure 5.** Honda Fit ICEV Eco-CACC-I fuel consumption for a speed limit of 25 mph.

The Honda Fit is a compact gasoline vehicle with a 97-HP engine. To examine whether ICEV optimal solutions are general or engine specific, a 2015 Cadillac SRX with a much more powerful engine of 230 HP was also tested. The same tests were conducted, assuming a connected automated Cadillac SRX equipped with the Eco-CACC-I controller. The simulation results for the two ICEVs were very similar. There were two differences. First, downstream of the intersection, the Cadillac could accelerate to the maximum allowed speed (speed limit) faster in the downhill direction, given that it had more engine power compared to the Honda Fit. Second, the energy consumption for the Cadillac was almost double that of the Honda Fit due to its larger size. However, the energy consumption curves across the solutions from minimum to maximum deceleration levels showed similar trends, demonstrating that the ICEV optimum strategies appear to be general. According to the test results for the two ICEVs, the optimal solutions produced by the Eco-CACC-I system for the downhill and uphill directions can be summarized as follows:

	- - Upstream—different deceleration levels do not change the ICEV's energy consumption during braking, so higher cruise speeds consume a similar amount of fuel.
	- - Downstream—higher cruise speeds at the stop bar result in less energy consumption downstream.
	- - Upstream—unlike the downhill direction, the vehicle consumes more energy to reach a higher cruise speed while traveling uphill.
	- - Downstream—higher cruise speeds result in less energy consumption downstream. Therefore, the optimal solution sits in the mid-range, depending on the vehicle's weight, engine power, and roadway slope.
