## 4 Results and Discussion
### The Impact of SLADS on Traffic Efficiency and CO\({}_{2}\) Emissions
#### 4.2.1 The Impact of SLADS on Traffic Delay under Different Driving Styles  
The influence of SLADS on traffic delay on the expressway and the secondary motorway under different aggressive style ratios of ICVs is shown in Figures 4 and 5, respectively. It is indicated in the Subgraph (a)-(e) in the two figures that the volume input in corresponding road types is the first service level, the third service level, the saturated service level, and the 20% and 40% oversaturated service level. For the expressway, when the aggressive style ratio of ICVs was lower than China's actual value (25.9%), shown by the regions above the red curve in each subfigure in Figure 4, SLADS did not show an improvement in traffic delay and even increased it. As the aggressive style proportion of ICV increased, however, SLADS could reduce traffic delay markedly, but this benefit gradually  
Figure 3: The impacts of SLADS on the average CO2 emissions per vehicle on the expressway (**a**) and the secondary motorway (**b**). decreased after the volume input outnumbered the saturated service level. Under the five different volume inputs in Figure 4a-e, when the aggressive style ratio and the penetration rate of ICVs both reached 100%, the average delay per vehicle was reduced by 40.01%, 57.03%, 89.44%, 85.86% and 45.51% separately, that is, 0.15 s, 1.11 s, 11.01 s, 15.06 s, and 8.49 s, respectively. At the same time, it can be observed that when the volume input is lower than the third service level and the aggressive style ratio of ICVs has reached a certain level, the delay reduction is achieved as long as the ICV penetration rate is bigger than 30%. When the volume input outstrips the saturated service level, although the aggressive style proportion of ICVs reaches the threshold for traffic delay reduction at low-to-medium service level (not higher than the third level), the traffic delay does not decrease quickly until the ICV penetration rate reaches a high level. This is because under the oversaturated service levels, the traffic density increases and the average traffic speed decreases. Vehicle lane changing, emergency braking or cautiously driving are likely to cause a moving bottleneck, which probably make the traffic flow enter a congested state. In addition, it is difficult for vehicles to achieve higher driving efficiency by changing lanes. Therefore, in order to significantly reduce traffic delay, the proportion of conservative styles in the traffic flow must be small enough and the driving style consistency of the entire traffic flow tends to be uniform. For the secondary motorway, when the volume input reached the first service level and the third service level, ICVs could not reduce traffic delay until the aggressive ratio exceeds 40%. When the volume input was not lower than the saturated service level, the  
Figure 4: The impacts of SLADS on traffic delay on 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**), the 20% (**d**) and 40% (**e**) oversaturated service level. Figure 5: The impacts of SLADS on traffic delay on the secondary motorways 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**), the 20% (**d**) and 40% (**e**) oversaturated service level. traffic delay could be reduced as long as the aggressive style ratio of ICVs outstripped 20%. At the same time, it is easy to find that once the aggressive style proportion of ICVs reaches the threshold for reducing the average traffic delay, the increase in ICV penetration rate can significantly reduce the average traffic delay.