Abstract: The commonly-used capacity calculation approaches for ramp junctions are mostly based on the American HCM method, It had been approved that the headways for vehicles following the Weibull distribution function at on-ramp junctions in urban freeway system. The paper examined the critical headway and following time by the modified drew method and the survey traffic flow data on-site. The gap-acceptance capacity calculating model was developed for on-ramp junctions of urban freeway, and the numerical integration method was used to solving the model. Finally, the capacity values were obtained in condition of different mainline design speeds and different acceleration lane lengths. The result indicated that the capacity value would grow with increase of the acceleration length and mainline design speed, and the capacity values for on-ramp junctions would approach basic freeway segments capacity values while the acceleration lengths beyond 400 meters.

Key words: urban freeway, on-ramp junction, headway, numerical integration method, capacity

摘要： 针对目前国内外匝道连接段通行能力计算以美国HCM为主的现状和不足，研究发现城市快速路入口匝道连接段车头时距服从Weibull分布规律，利用改进的Drew方法及实际现场调查交通流数据确定了临界车头时距和随车时距，建立了城市快速路入口匝道连接段通行能力的间隙接受计算模型，并利用数值积分法进行计算和求解，从而得到了主线不同设计速度及不同加速车道长度条件下的城市快速路入口匝道连接段可能通行能力值。研究结果表明，快速路匝道连接段通行能力随加速车道长度和主线设计速度的增加而增加，变速车道长度大于400 m时通行能力值趋近于基本路段通行能力。

关键词: 城市快速路, 入口匝道连接段, 车头时距, 数值积分法, 通行能力