Roundabout implementations at traditional intersections have been shown to be effective at reducing severe crashes. Roundabouts have also been implemented at interchange ramp terminals; however, limited research is available. In this study, 25 roundabout ramp terminal implementations were evaluated. The methodological approach consisted of Empirical Bayes for safety effectiveness and crash cost changes, crash type weighted distribution, crash rate analysis of bypass configuration, and cost of implementation. Roundabouts were effective at reducing fatal and injury crashes when replacing existing interchange diamond ramp terminals: 65% reduction for roundabouts replacing stop-controlled ramp terminals and 41% reduction for roundabouts replacing signal-controlled ramp terminals. Observed crash type weighted distributions are provided to visualize the frequency and location of crashes within roundabout ramp terminals for design considerations. Exit ramp and outside crossroad approaches with right-turn bypass showed significantly lower crash rates than designs without bypass. The crash cost analysis showed that roundabouts replacing diamond ramp terminals yielded crash cost savings of between $95,000 and $253,000 per site per year (69% to 54% decrease in crash costs). Considering crash costs savings only, the cost of implementation should be less than $1.9 million for a roundabout replacing a stop-controlled ramp terminal and less than $5.1 million for a roundabout replacing a signal-controlled ramp terminal to accomplish benefit-cost ratios greater than one for a service life cycle of 20 years. Costs are in 2019 dollars.

传统交叉路口的回旋处措施已被证明可有效减少严重的撞车事故。回旋处也已在互换坡道终点站实施；但是，研究还很有限。在这项研究中，对25个回旋处的匝道终端实施方案进行了评估。该方法学方法包括用于安全有效性和碰撞成本变化的经验贝叶斯，碰撞类型加权分布，旁路配置的碰撞率分析以及实施成本。替换现有的互换菱形坡道终端时，回旋处可有效减少致命和伤害事故：替换停站控制的坡道终端，回旋处减少65％，而替换信号控制的坡道终端，回旋处减少41％。出于设计考虑，提供了观察到的碰撞类型加权分布，以可视化在回旋匝道终端内的碰撞频率和位置。与没有旁路的设计相比，带有右转旁路的出口匝道和外部十字路口的碰撞率显着降低。事故成本分析表明，使用环形交叉路口代替菱形坡道码头每年可为每个站点节省95,000至253,000美元的事故成本（事故成本降低69％至54％）。仅考虑到事故成本的节省，回旋处更换停机控制的坡道终端的实施成本应低于190万美元，而回旋处更换信号控制坡道终端以实现高于成本的收益成本应低于510万美元。使用寿命为20年。成本以2019年美元计。