###### Abstract  
There are big differences between the driving behaviors of intelligent connected vehicles (ICVs) and traditional human-driven vehicles (HVs). ICVs will be mixed with HVs on roads for a long time in the future. Different intelligent functions and different driving styles will affect the condition of traffic flow, thereby changing traffic efficiency and emissions. In this paper, we focus on China's expressways and secondary motorways, and the impacts of the'single-lane automatic driving system' (SLADS) on traffic delay, road capacity and carbon dioxide (CO\({}_{2}\)) emissions were studied under different ICV penetration rates. Driving styles were regarded as important factors for scenario analysis. We found that with higher volume input, SLADS has an optimizing effect on traffic efficiency and CO\({}_{2}\) emissions generally, which will be more significant as the ICV penetration rate increases. Additionally, enhancing the aggressiveness of driving behavior appropriately is an effective way to amplify the benefits of SLADS. intelligent connected vehicle; single-lane automatic driving system; China's motorway; traffic efficiency; CO\({}_{2}\) emissions +
Footnote †: journal: Applied Sciences  
as having a direct impact on ICVs and an indirect impact on energy consumption and emissions [5]. At present, many scholars have conducted studies on the influences of ICVs on transportation efficiency, energy consumption and emissions, but the conclusions are significantly different. Based on the Kalman filter algorithm, [PERSON] et al. developed a method to estimate the average speed of expressway sections using data from ICVs with low penetration rate (not more than 10%), but unfortunately it did not further analyze the specific impacts [6]. [PERSON] et al. believe that when the penetration rate of the adaptive cruise system (ACC) reaches 50%, ICVs can increase the traffic volume by 20% at expressway merging areas and improve the total travel distance per unit time by 3.6 km [7]. Focusing on the basic two-lane section of the expressway, [PERSON] et al. analyzed the impacts on the road capacity of two kinds of ICVs under different penetration rates. The two kinds of ICVs are autonomous vehicles and cooperative vehicles, which are developed with different technical routes. It was found that autonomous vehicles have almost no impact on the road while the cooperative vehicles can effectively shorten the car following distance so as to improve road capacity [8]. [PERSON] et al. have the same views as [PERSON] et al. on the mechanism of the impact of ICVs on traffic flow. Through simulation research, they found that, as for expressways, ICV will exert a negative impact on road capacity when its penetration rate is lower than 40%. However, the road capacity will be significantly improved if the ICV penetration rate is over 40% and the improvement effect will be more apparent with the increase of the road speed limit [9]. In order to promote the rapid implementation of ICVs, [PERSON] et al. studied the impact of dedicated lanes for ICVs on expressways' traffic flow in terms of traffic control. They claimed that the number of dedicated lanes should correspond to the ICV penetration rate [10]. Considering the road safety law and the huge expressway mileage, however, laying a large area of dedicated lanes for ICVs is probably not realistic in China in a short period of time. [PERSON] et al. studied the impact of ICVs on traffic flow characteristics and energy consumption from multiple dimensions such as technical routes, powertrain types, penetration rates, driving styles and road scenes. They found that ICVs with an aggressive style can reduce carbon dioxide (CO\({}_{2}\)) emissions by 26%, increase the average speed, reduce travel delay, and improve traffic capacity. On the contrary, ICVs with a conservative style will have the opposite effect [11]. [PERSON] et al.