Abstract
With the emerging application of low-level driving automation technology, heterogeneous traffic flow mixed with human-driven vehicles and low-level autonomous vehicles is dawning. In this context, it is imperative to investigate its effect on mixed traffic flow. As a key component for adaptive cruise control (ACC) which is a practical low-level application of driving automation, the time gap policy determines the dynamic of ACC-equipped vehicles and plays a crucial role in traffic flow stability and efficiency. There are two main time gap policies used for ACC at present, namely, constant time gap (CTG) policy and variable time gap (VTG) policy. In this study, we carried out a detailed comparison between these time gap policies to investigate their potential effect on mixed traffic flow, where the analytical- and simulation-based approaches are both considered. Analytical results show that VTG policy is superior to CTG policy in stabilizing the mixed traffic flow. In addition, numerical simulations are also conducted and simulation results further support the analytical results. As for throughput, there is no difference between CTG policy and VTG policy in analytical progress when the same time gap is set at the equilibrium. However, simulation results based on an on-ramp scenario show that the throughput of mixed traffic flow with VTG policy is slightly higher than that of CTG policy. Meanwhile, the scatter of mixed traffic flow with VTG policy in the flow-density diagram gradually clusters in the middle range of density (i.e., 20–40 veh/km) with the increase of the penetration rates of ACC vehicles, where the traffic flow operates more efficiently. These results indicate that VTG policy is better than CTG policy when designing controllers for ACC in the context of traffic flow operation and control.
Highlights
With the development of high-precision sensing and lowlatency communication technologies, connected and automated vehicles (CAVs) are the most promising approach to improve traffic safety and efficiency
Based on different target spacing strategies, the adaptive cruise control (ACC) control scheme can be divided into constant spacing policy, variable spacing policy with constant time gap (CTG), and variable spacing policy with variable time gap (VTG)
Where a is the calculated acceleration for ACC vehicles, s, v, and Δv are distance gap, speed, and relative speed of ego vehicle, respectively, s0 represents the standstill distance between successive vehicles, th is the desired time gap for ACC vehicles, and k1 and k2 are control gains
Summary
With the development of high-precision sensing and lowlatency communication technologies, connected and automated vehicles (CAVs) are the most promising approach to improve traffic safety and efficiency. Very little studies have been designed to investigate the stability of mixed traffic flow considering a VTG policy for ACC. Too little work has been devoted to the stability and throughput analysis of VTG policy in the mixed traffic flow environment It is still unclear which time gap policy is superior in terms of stabilizing mixed traffic flow and improving road capacity analytically. The intelligent driver model is considered to capture the dynamic of HDVs. en, the stability of mixed traffic flow considering different time gap policies is derived analytically. A detailed comparison between different time gap policies for ACC on the stability and throughput analysis of mixed traffic flow are investigated in both analytical and simulation-based ways.
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