## 4 Results and Discussion
### The Impact of SLADS on Traffic Efficiency and CO\({}_{2}\) Emissions
#### 4.2.3 The Impact of SLADS on CO\({}_{2}\) Emissions under Different Driving Styles  
The influences of SLADS on CO\({}_{2}\) emissions on the expressway and the secondary motorway under different aggressive style ratios of ICVs are shown in Figures 8 and 9 separately. Subgraph (a)-(e) of the two figures show the volume input in the corresponding road type for the first service level, the third service level, the saturated service level, and the 20% and 40% oversaturated service level. On the expressway, when the volume input is at the first and the third service level, no matter how the aggressive style proportion of ICVs changes, SLADS cannot reduce the average CO\({}_{2}\) emissions per vehicle and may even cause an increase. It is observed in Figure 8a that there is fluctuation in the curves for the average CO\({}_{2}\) emissions per vehicle for different aggressive style ratios of ICVs. However, the fluctuation ranges under the same aggressive style ratios do not exceed 10% of the benchmark value, which can be attributed to the difference in vehicle distribution in VISSIM. At the saturated service level, with the gradual increase of ICV penetration rate, the average CO\({}_{2}\) emissions per vehicle could be remarkably reduced by about 10.05% if the aggressive style proportion of ICVs reached the Chinese actual value. When the volume input was equal to the 20% and 40% oversaturated service level, it could be significantly reduced by appropriately raising the aggressive style ratio (up to 60%). Compared with the standard situation where the ICV penetration rate is 0 and the aggressive style ratio is the same with the Chinese actual value, it could be reduced by up to 25.03% and 42.58%, respectively. Figure 7: The impacts of SLADS on road capacity of the secondary motorway under different driving styles with the volume input being equal to the saturated service level (**a**), 20% oversaturated service level (**b**) and 40% oversaturated service level (**c**). For the secondary motorway, when the traffic input was at the first and the third service levels, there was an upward trend in the average CO2 emissions per vehicle as the aggressive style proportion of ICVs increased. What has to be noted is that there is a regular abnormal drop in the average CO2 emissions per vehicle shown in the red circle in Figure 9a. This is probably caused by the difference in vehicle distribution in the simulation software, the results of which should consequently not be adopted. When the volume input was at the saturated service level, the 20% oversaturated service level and the 40% oversaturated service level, there were decreasing intervals in the average CO2 emissions per vehicle if the aggressive style ratio was not smaller than 40%. In the decreasing interval, compared with the standard situation where the ICV penetration rate is 0 and the aggressive style ratio is the same as the Chinese actual value, it could be reduced by 7.24%, 12.64%, and 4.40%, respectively. Figure 8: The impacts of SLADS on the average CO2 emissions per vehicle of the expressway under different driving styles with the volume input being equal to the first service level (**a**), the third service level (**b**), the saturated service level (**c**), and the 20% (**d**) and 40% (**e**) oversaturated service level. Figure 9: The impacts of SLADS on the average CO2 emissions per vehicle of the secondary motorway under different driving styles with the volume input being equal to the first service level (**a**), the third service level (**b**), the saturated service level (**c**), and the 20% (**d**) and 40% (**e**) oversaturated service level. In addition, regardless of the road types, when the traffic input was not lower than the saturated service level, the average CO\({}_{2}\) emissions per vehicle declined at first but then increased with the increase of ICV penetration rate.