中文摘要：

交叉口是城市道路交通系统的重要组成部分．对交叉口的改造是提高路网通行能力和安全水平的有效手段之一，其中，环岛改信控是当前我国许多中小城市提高道路通行能力的改造方式．理论上，当交通量达到一定程度，情控比环岛的通行效率更高，但由于信控模式会带来更多的交通冲突，可能降低交叉口的安全水平．本文综合考虑通行效率和安全水平，建立环岛改信控评价模型，将通行能力、延误、停车次数、排队长度以及服务水平作为通行效率的评价指标，冲突点数及其恶性程度作为安全水平的主要影响因素，提出两种类型交叉El的综合评价方法，为环岛改倩控提供科学评价手段．以涟源市五马广场改造方案为例，验证了此类改造方案的可行性及有效性，为工程实践提供理论指导．

英文摘要：

Traffic intersection is an important part of urban road traffic systems and engineering improve- ment for intersections is one of the effective means to improve the capacity and safety level of overall road network. Converting roundabout into signalized intersection is a way to improve traffic capacity, which is widely used in many small and medium-sized cities of China nowadays. In theory, when traffic volume rea- ches a certain level, signalized intersection is more efficient. However, since more traffic conflicts are asso- ciated with signalized intersection, the safety level may decline. This study presents a comprehensive evalu- ation for both traffic efficiency and safety level for the two types of intersection, in which traffic capacity, delay, number of stops, queue length and level of service were taken as the evaluation indexes of traffic effi- ciency; and accident rate, number of conflict points and their degrees of malignancy were considered as the main influence factors of safety level. In the case study of Wuma Square in Lianyuan City, the feasibility and effectiveness of converting roundabout into signalized intersection were demonstrated, which can provide theoretical guidance for the engineering practices.