张飞飞
外环线在城市发展及交通系统中发挥着重要的作用，越来越多的城市通过修建外环线来引导城市合理布局并进一步缓解交通压力。而合理的规划设计是外环线有效运行的前提，有必要将相关理论与工程实践相结合，对外环线规划设计中的相关问题进行研究，实现外环线与城市快速系统的协调配合。
在总结国内外典型案例的基础上，分析外环线的路网关系及功能特征，进一步对外环线进行界定并总结其特点，借助路网布局分析外环线与城市形态的适应性，在总结分析天津市外环线改建面临问题的基础上，对交通功能、线位调整、设计标准及规模及交通衔接进行研究。
环线为中心区的保护壳、外环线与区域间的联系、外环线与功能组团间的联系、外环线与其他道路的交通衔接、外环线与疏港通道五个方面分析天津市外环线的功能；通过分析线位与用地及路网的关系，对天津市外环线线位进行调整，并进一步分析外环线与快速内环的线位关系；分析了外环线的设计标准及规模，包括型式等级、车速、车道数量及宽度，研究了交通组成对路段通行能力的影响，通过设置大小型车专用车道实现大小型车分离，并对车道宽度进行分析，之后根据相关交通需求预测结果确定天津市外环线设计标准；交通衔接部分着重对出入口的间距、数量及位置进行研究，确定外环线出入口及互通立交的间距，利用路网布局理论及节点重要度确定互通立交数量及位置，根据交通线吸引特性理论分析了路段出入口与立交的关系，并分析了沿线功能组团、主次干道位置与主辅路出入口的关系，通过分析主辅路出入口数量对主线交通量及主线运行效率的影响，建立了交通效益-出入口数量函数；最后对天津市外环线交通衔接进行分析，并结合芥园西道-津沧快速路路段对主辅路出入口进行设计。
关键词：城市交通，路网布局，外环线，设计标准，交通衔接
Outer circle-road plays an important role in the transportation system and urban development, in order to relieve traffic congestion and rationalize the layout of the city, more and more cities build outer circle-road. Only with rational planning and designing, could outer circle-road be effective, it is necessary to research the relative problems and to combine theory with practice, and then coordination between outer circle-road and other freeways can be achieved.
This paper summarizes the network relations and functions of outer circle-road based on the canonical cases home and abroad, and then analyzes the suitability of outer circle-road for urban forms. After summarizing the reconstruction problems of Tianjin outer circle-road, this paper researches the traffic function, rout adjustment, standards of designing and node traffic connection.
In the paper, traffic functions of Tianjin outer circle-road are analyzed from five respects: outer circle-road is the protective shell of the downtown area, the connection between outer circle-road and other cities, the relationship of outer circle-road and suburbs, node connection between outer circle-road and other roads, the role outer circle-road plays in harbor transportation. Rout position adjustment of Tianjin outer circle-road is given after analyzing the relationship between rout position and land use, as well as the relationship between rout position and road network. Then this paper analyzes the standards of designing of outer circle-road, including road grade, speed, lanes and width. On the basis of research on the factors affecting capacity, the paper proposes setting heavy vehicle lane and car lane with different lane width, designing standards of Tianjin outer circle-road is given based on the traffic demand forecasting. In the traffic connection part, the distance, quantity and location of ramps are researched, the distances of ramps and intersections is given, using the road network and node importance theory to determine the quantity and location of ramps, a function of traffic benefit and ramp quantity is introduced. At last the traffic connection of Tianjin outer circle-road is analyzed, and the ramps design between west jieyuan road and jincang expressway is given.
Key Words: urban transport, road network design, outer circle-road, designing standards, node traffic connection
