In what circumstance is a height of 28 inches required for tubular markers?

A height of 28 inches for tubular markers is required when they are used at night or at high speeds to enhance visibility and ensure safety in work zones. This specification is critical because the challenges posed by reduced visibility in low light conditions or the increased speeds associated with certain roadways necessitate a more pronounced marker height. Higher markers are more easily seen by drivers, allowing them to react properly to the presence of a work zone or any hazards.

In addition, the requirement for increased height in these circumstances helps prevent accidents, as drivers can more readily identify the markers from a greater distance. The added visibility is essential for roadway safety, ensuring that markers serve their purpose effectively when they are most needed.

Other scenarios, such as being stacked, used during the day, or mounted on vehicles, may not require the same height for effective visibility, hence the specification is particularly important under challenging conditions like nighttime operation or on high-speed roads.