What is the minimum distance that the message on portable changeable message signs should be visible?

The minimum distance for visibility of the message on portable changeable message signs is 650 feet. This distance ensures that drivers have sufficient time to see, read, and react to the information being presented by the sign, which is critical for maintaining safety within work zones or areas where driving conditions may be altered.

This guideline is based on studies and standards that account for typical driving speeds, allowing for an appropriate reaction time. At 650 feet, drivers can begin to prepare for any necessary changes in their driving behavior, whether that involves slowing down, merging, or navigating around obstacles safely. The use of portable changeable message signs at this visibility range maximizes their effectiveness in traffic control situations.