What should a driver do when approaching a roundabout?

When approaching a roundabout, the driver should yield to traffic already in the roundabout. This is because vehicles circulating within the roundabout have the right-of-way, allowing for smooth traffic flow and minimizing potential collisions. Yielding ensures that drivers can safely enter the roundabout without disrupting the movement of those already in it.

This practice not only helps maintain safety but also promotes efficient traffic management. Roundabouts are designed to reduce the number of conflict points and can significantly decrease traffic delays when drivers yield appropriately.

In contrast, the other options do not follow the established traffic rules for roundabouts. Proceeding straight through without stopping may lead to accidents if a driver doesn't respect the right-of-way of vehicles already circulating. Signaling left while entering might confuse other drivers and is not the standard practice; the common protocol is to signal your exit from the roundabout instead. Lastly, increasing speed to merge can create hazardous conditions, as it disregards the need to yield and can result in unsafe merging behavior.