From OpenStreetMap Wiki
Describing the kind of a junction.
This key describes how a specific junction is constituted.
- supervised=yes can be used in combination with the
junctiontag when a police officer ( Verkehrsposten) stands in the middle of the junction to direct traffic. Sometimes there is a small platform on which the officer can stand. Such supervised junctions can no longer be found in industrialized countries (traffic lights are used instead), but they are still common in countries such as Bhutan or North Korea.