Abstract: There are frequent confluence and diffluence operations at roundabout weaving sections. The operation performances are complicated because the entry vehicles of turn-left and run-straight travel around the circle center. On the basis of the Shuma square roundabout survey using video cameras, some parameter performances are analyzed, which includes the velocity distribution, the distance distribution of changing lane, the headway distribution of confluence vehicles, and vehicles on circulating lanes, as well as the application of accepted headways. Besides, some conclusions are drawn, for example, the vehicle velocity of outer circulating lane is larger than the inner circulating lane; the confluence vehicle velocity is smallest; the diffluence operation occurs later than the confluence operation; the confluence vehicle velocity has a tendency to increase with the accepted headway increase; the posterior gap is usually larger than the frontal gap in one accepted headway; the equivalent critical gap of multilane roundabouts is smaller than the critical gap of single-lane roundabouts.

Key words: urban traffic, roundabout, weaving section, confluence, headway, critical gap

摘要： 由于环形交叉口入口车辆直行和左转的绕行而避免了流线冲突，交织区存在着大量的分流、合流行为，车流运行特性复杂. 通过对环形交叉口交织区的摄像调查，测算并分析在该区域的合流与分流运行行为的速度分布、换道位置分布，合流车与环道上前后车的车头时距分布，以及可插间隙的利用等规律，研究发现环形交叉口交织区运行行为具有以下特性：外环道车速比内环道的车速大，合流车的车速最低；分流行为发生于合流行为之后；当可插间隙增大时，合流车速有增大的趋势；对于较小的可插间隙，通常后车时距大于前车时距；多车道环形交叉口的当量车流的临界间隙小于单车道环形交叉口临界间隙.

关键词: 城市交通, 环形交叉口, 交织区, 合流, 车头时距, 临界间隙