What is the purpose of a central apron in a roundabout?

The central apron in a roundabout is designed to accommodate the rear wheels of larger vehicles, allowing them to ride over this area. This feature helps facilitate the navigation of larger vehicles, such as trucks and buses, through the roundabout without the risk of them striking the central island or causing congestion. By allowing the rear wheels to mount the apron, it enables these larger vehicles to make tight turns while ensuring that they can operate safely within the confines of the roundabout.

In contrast, the other choices do not appropriately describe the function of a central apron. For example, creating an extra lane for all traffic is not the purpose of an apron; rather, its primary function is to assist in the movement of larger vehicles. Adding a visible finish to the edges is more about aesthetics than functionality. Similarly, the notion of creating an additional lane does not align with the structural design of a roundabout, which inherently manages traffic flow through its circular shape and designated lanes.