The curve does more than set direction
A roundabout’s center island blocks a straight path through the junction. To reach an exit, a driver must steer around it, and the entry is angled so traffic joins the circulating stream rather than crossing it. In the United States, vehicles travel counterclockwise around the island; other countries drive on the opposite side of the road and circulate the other way.
That bend also shapes speed. Drivers approach on a curved path instead of racing straight toward a crossing, making it harder to enter at high speed. The island and the road’s raised edges—often called splitter islands—guide vehicles into the intended path and can separate entering traffic from traffic leaving the circle.
Why yielding fits the layout
At the entrance, drivers give way to vehicles already circulating. That priority lets the stream continue without a signal assigning turns in timed phases. A driver waits for a usable gap, enters, then follows the curve to the chosen exit. The geometry makes the expected movement visible: traffic is coming from one side, and nobody should be cutting straight across the center.
The design is not simply a circle painted on a road. Its entry angle, curve, and lane arrangement have to make drivers slow and choose a path clearly. If the curve is too easy to drive straight through, the island may not slow traffic as intended; if lanes are confusing, drivers can hesitate or change lanes abruptly.
A different kind of intersection tradeoff
Because vehicles merge and separate rather than cross through the middle, roundabouts reduce the number of places where paths intersect. They can keep traffic moving when gaps are available, but drivers may still wait during heavy demand, and pedestrians have to cross the approaches rather than the circulating roadway. The center island is therefore both a physical barrier and a traffic organizer: it turns a junction’s movements into a sequence of bends, yields, and exits.
