Arrow panels in work zones show a rectangle or line to indicate:

Arrow panels in work zones are specifically designed to communicate important information to drivers about safely navigating through or around construction areas. When an arrow panel displays a rectangle or line, it indicates that drivers should proceed with caution. This signal serves as a reminder to be alert for potential hazards and changes in traffic patterns that may be present due to the work being conducted.

The other options would correspond to different messages or signals that might be indicated by other shapes or patterns. For example, messages about an open lane or a road closure would typically use different symbols or configurations on the arrow panel to convey those specific instructions. The optimal understanding of these signals contributes to safer driving conditions and assists with smooth traffic flow in areas where construction is occurring.