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.

中文翻译：

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自适应巡航控制对混合交通流的影响：恒定时间间隔政策与可变时间间隔政策的比较

随着低水平驾驶自动化技术的新兴应用，混合了人类驾驶车辆和低水平自动驾驶汽车的异构交通流开始出现。在这种情况下，有必要研究其对混合交通流的影响。作为自适应巡航控制 (ACC) 的关键组件，这是驾驶自动化的实际低级应用，时间间隔策略决定了配备 ACC 的车辆的动态，对交通流的稳定性和效率起着至关重要的作用。目前ACC主要采用两种时隙策略，即恒定时隙（CTG）策略和可变时隙（VTG）策略。在这项研究中，我们对这些时间间隔政策进行了详细比较，以研究它们对混合交通流量的潜在影响，其中同时考虑了基于分析和模拟的方法。分析结果表明，VTG 策略在稳定混合交通流方面优于 CTG 策略。此外，还进行了数值模拟，模拟结果进一步支持了分析结果。至于吞吐量，在均衡时设置相同的时间间隔时，CTG 策略和 VTG 策略在分析进程上没有差异。然而，基于入口匝道场景的仿真结果表明，采用 VTG 策略的混合交通流的吞吐量略高于 CTG 策略的吞吐量。同时，随着ACC车辆渗透率的增加，流密度图中带有VTG策略的混合交通流的分散度逐渐聚集在中等密度范围内（即20-40 veh / km），交通流运行更有效的地方。这些结果表明，在交通流操作和控制的背景下为 ACC 设计控制器时，VTG 策略优于 CTG 策略。