How many inches above the roadway should the top of a vertical panel be?

The correct height for the top of a vertical panel above the roadway is 36 inches. This specification is established to optimize visibility for drivers, ensuring that the panels effectively communicate important information, such as warnings or direction changes. At this height, the panels are placed in a position that can be clearly seen by approaching vehicles, even in varying weather conditions or during different times of day. This height aligns with standard safety guidelines, which aim to reduce the likelihood of accidents in work zones by maintaining clear communication through signage.

The other potential heights may not provide the same level of visibility or could even become obstructed by vehicle dimensions, thereby decreasing their effectiveness. Therefore, adhering to the specified height of 36 inches is crucial for maintaining safety in work zones.