What characterizes a high visibility work zone?

A high visibility work zone is primarily characterized by the use of reflective materials. This feature is crucial because reflective materials enhance the visibility of signs, barriers, and other traffic control devices both day and night. By ensuring that these elements are easily seen, they help drivers adjust their speed and approach with caution, thereby improving safety for both workers and motorists in the vicinity of the work zone.

While the other choices may contribute to overall safety or functionality within a work zone, they do not specifically define its visibility. For instance, portable lighting can aid visibility at night but does not contribute to persistent visibility like reflective materials do. Likewise, a simple layout can ease navigation through a work zone, and low traffic volume may reduce the risk of accidents, but these factors do not enhance the visibility of the work zone itself. The essential characteristic of high visibility is the presence and effective use of reflective materials.