环形回车道（英语：Balloon Loop），又称单向循环，灯泡线，用以供列车直接折返而无需转轨甚至无需停车。环形回车道对旅客列车、货运列车（如煤车）很有用。

环形回车道亦常见于路面电车系统。很多（尽管不是所有）路面电车系统使用单车头车辆并仅有一侧有门，必须在终点处调头。

优点是：有利于列车运行速度发挥，消除了因折返作业而形成的线路通过能力限制条件。

缺点是：占地面积较大，尤其是在地下修建难度更大，投资较高；丧失了一端停车维护保养检查的机动线路，对车辆技术要求与运行组织要求更高。线路机动性下降，线路延伸可能性甚微，一般只适用于线路较短，线路延伸可能较小且该端点站在地面的情况。

A balloon loop or turning loop allows a rail vehicle or train to reverse direction without having to shunt or even stop. Balloon loops can be useful for passenger trains and unit freight trains such as coal trains.

Balloon loops are common on tram or streetcar systems. Many streetcar and tram systems use single-ended vehicles that have doors on only one side and must be turned at each end of the route, or else haul trailer cars with no driver's cabin in the rear car.