What is one common feature of roundabouts?

Roundabouts are designed to facilitate the smooth flow of traffic by organizing how vehicles enter and navigate through intersections. A key feature of roundabouts is that traffic must yield to vehicles that are already in the roundabout, which means that drivers entering the roundabout typically yield to their right. This design reduces the likelihood of serious accidents and improves overall traffic efficiency by minimizing stops and allowing a continuous flow of vehicles.

The other options provided do not accurately reflect the fundamental characteristics of roundabouts. For instance, allowing two-way traffic contradicts the intended one-way circulation of roundabouts, which helps to prevent confusion and potential collisions. The notion that drivers should always turn left is incorrect, as roundabouts generally require drivers to proceed in a circular direction to the right; thus, left turns are made by following the roundabout's curve. Finally, the requirement that all vehicles must stop before entering contradicts the purpose of roundabouts, which is to maintain flow; vehicles only stop if necessary when yielding to traffic already in the roundabout. Thus, the yielding to the right is an essential rule that defines the operation of roundabouts.