When mounting a secondary sign below a post-mounted roadside sign, what is the minimum height for the secondary sign?

The correct choice regarding the minimum height for mounting a secondary sign below a post-mounted roadside sign is based on safety and visibility standards outlined in traffic control guidelines. For secondary signs, the height should be set at a minimum of 6 feet above the ground to ensure they are clearly visible to drivers and do not obstruct sight lines. This height helps in making sure that the signs are above the average vehicle height, preventing any obstructions by typical roadside elements.

Choosing a height of 6 feet strikes a balance between visibility for both vehicles and pedestrians and ensures compliance with regulatory standards that aim to maintain effective communication of traffic information. When signs are mounted too low, they risk being hidden from the view of motorists, which can lead to confusion and potentially dangerous situations. Hence, the minimum height of 6 feet is necessary to establish a standard that successfully promotes safe and effective traffic control in work zones.