Abstract: Currently，some exit ramps of elevated roads in Shanghai are so crowd at peak time that they face to be taken of engineering measures. Boundary conditions of engineering implementation at zone of exit ramp of road are studied by using VISSIM software to model. Firstly，the evacuation capability of the exit (the largest traffic volume to leave the ramp and to get through the intersection ahead) is determined on the condition that the queue length of vehicle at the zone of exit ramp does not go back to the main line，which establishes theoretical foundation for the control and organization of exit ramp. Then，with the combination of existing traffic demand，the sufficient conditions and necessary conditions of engineering implementation are determined quantitatively，which can provide a theoretical basis for the engineering implementation at zone of exit ramp of elevated roads in Shanghai or other cities in China.

Key words: exit ramp of elevated road, boundary conditions of engineering implementation, VISSIM simulation, queue length, evacuation capability

摘要： 针对目前上海市交通高峰期部分出口匝道拥挤严重而面临可能采取工程措施的情况，利用VISSIM仿真软件 建模进行出口匝道区域工程措施实施的边界条件研究。以模型中出口匝道车辆排队长度不回溯至主线为条件，确 定某个出口匝道的疏散能力(能离开该出口匝道并通过前方交叉口疏散的最大交通量)，为今后出口匝道的组织和 控制奠定理论基础，并结合现状交通需求，定量确定实施工程措施的充分条件和必要条件，给上海乃至全国高架道 路出口匝道区域工程措施实施与否提供理论依据。

关键词: 高架道路出口匝道, 工程措施边界条件, VISSIM仿真, 排队长度, 疏散能力