Many traffic accidents occur in the merging and diverging area of expressway and ramp, which forms the combination bottleneck of traffic accidents and ramp at the same time, and has a negative impact on traffic flow. Based on the classic KKW (Kerner–Klenov–Wolf) model of three-phase traffic flow theory, this paper introduces traffic accident and defines the priority rule of vehicle lane changing in front of the accident site, proposes the traffic flow model of expressway ramp system under the accident conditions, and simulates and analyzes the impact of traffic accident on the traffic flow under the open boundary condition. It is found that the congestion caused by the accident will not propagates to the upstream basically under the free flow, but will obviously propagate to the upstream under the synchronized flow. Besides, the combined bottleneck effect of accidents and on-ramp can be clearly found under synchronized flow. This work is helpful to understand the mechanism of traffic congestion and provide reference suggestions for traffic control under accident conditions.

高速公路与匝道的合并与分叉区域发生了许多交通事故，同时形成了交通事故与匝道的结合瓶颈，对交通流量产生了负面影响。基于经典的三相交通流理论KKW（Kerner–Klenov–Wolf）模型，本文介绍了交通事故并定义了事故现场前方车道变更的优先规则，提出了高速公路匝道的交通流模型。事故条件下的系统，并模拟和分析在开放边界条件下交通事故对交通流的影响。研究发现，事故引起的拥塞基本上不会在自由流下传播到上游，而是明显在同步流下传播到上游。除了，在同步流下，可以清楚地发现事故和匝道的综合瓶颈效应。这项工作有助于了解交通拥堵的机理，并为事故情况下的交通控制提供参考建议。