In the U.S. Aids to Navigation System, red and green horizontally banded buoys mark _______.

Red and green horizontally banded buoys are used in the U.S. Aids to Navigation System to indicate junctions or bifurcations in navigational channels. These buoys serve as important navigational aids that guide mariners when they encounter a point where the waterway splits into two or more directions.

The red buoys generally represent the port side (left) when entering a channel, while the green buoys indicate the starboard side (right). The specific horizontal banding of these buoys enhances visibility and aids the mariner in making the correct navigational decision as they choose which waterway to follow. This system effectively communicates to the navigator the safe paths available and helps to mitigate the risks of navigating in complex waterways where multiple routes may exist.

While other options describe different types of navigational aids or areas, they do not specifically pertain to the role of red and green horizontally banded buoys in marking junctions or bifurcations.