考虑自适应巡航车辆影响的上匝道系统混合交通流模型

A hybrid traffic flow model with considering the influence of adaptive cruise control vehicles and on-ramps

在考虑自适应巡航(adaptive cruise control,ACC)车辆的交通流模型的基础上,建立了考虑ACC车辆影响的上匝道系统混合交通流模型,研究ACC车辆引入对上匝道交通系统交通流的影响.为了描述ACC车辆和手动驾驶车辆在交通流运行中的差异,分别构建了基于常车头时距原则的ACC车辆跟驰子模型和手动驾驶车辆MCD元胞自动机子模型;基于上匝道车辆合流驶入主线的需求,建立了换道子模型,引入了表征驾驶员换道心理的参数λ.通过对混合交通流模型进行数值模拟发现,ACC车辆的混入可以有效改善上匝道系统交通流的运行,降低合流等事件对于交通流运行的影响,抑制交通拥堵的时空范围及拥堵强度,提高交通流的平均速度和流量.此外在混合交通流模型中,ACC车辆期望车头时距Hd的减小与换道心理参数λ的增大均可以提高混合交通流运行的速度和流量,而合流区长度lw对混合交通流影响则因上匝道车辆驶入概率的不同而存在差异.

Recently, autonomous vehicles and the relevant studies have attracted much attention. Adaptive cruise control（ACC）, which is a kind of cruise control system for vehicles, automatically adjusts the vehicle speed to maintain a safe distance from vehicles ahead. Since the vehicle with ACC（called ACC vehicles） is semi-autonomous, the performance of ACC vehicle must be quite different from that of manual vehicle. The characteristics of traffic flow with ACC vehicles should be carefully investigated, especially when the traffic system is a bit complicated, such as on-ramp system.The primary objective of this paper is to propose a traffic flow model to simulate the traffic flow with considering the influence of ACC vehicles and on-ramps. Based on the model proposed by Yuan in 2009 [Yuan Y M 2009 Ph. D.Dissertation（Hefei： University of Science and Technology of China）], a hybrid traffic flow model with considering the influence of ACC vehicles and on-ramps is developed. Considering the differences between ACC and manual vehicles, a car-following sub-model based on constant time headway principle is developed for ACC vehicles, while an MCD cellular automata sub-model is proposed for manual vehicles. Besides, a new parameter, λ, is introduced to show different psychologies of drivers when changing lane from on-ramp to main road. The lane-changing model for vehicles on-ramp is developed as well. At the end, numerical simulation is demonstrated to study the influence of ACC vehicles on traffic flow at on-ramp, and to reveal the influence of parameters on the proposed hybrid model（i.e., the length of merge area,the desired time headway of ACC vehicle and λ） on model performance.The results of this paper are as follows. 1） When the ACC vehicles exist in a traffic system, the performance of traffic flow in a on-ramp area is improved： the influence of merged vehicles on main road is reduced, and the average speed and volume are increased. 2） The increase of ACC vehicles can help to alleviate traffic congestion in both congestion duration and scope aspects. 3） The newly proposed hybrid model is sensitive to the length of merge area lw, the desired time headway of ACC vehicle Hdand lane-changing psychology parameter λ： the decrease of Hdand the increase of λcan both improve the average speed and volume of traffic flow. In addition, when the volume of on-ramp is small, the speed and volume of main road can be improved by enlarging lw. When the volume of on-ramp is large, a small lw will be better for traffic flow.