A message board is a large electronic display used to inform foot or vehicle traffic of an important safety notification or update relevant to a specific area of travel. They are usually visible from the street or highway. These signs are generally positioned on the shoulder of a road or highway or attached to bridges over highways for clear visibility.

Much like a message board, an arrow board is a large electronic sign that displays directional arrows informing drivers of a change or shift in direction regarding the flow of traffic. They’re commonly used to redirect drivers to detour routes or inform drivers of a lane drop on the road through a work zone. These signs are usually positioned on the shoulder of a road and are sometimes found in the median.

A message board becomes necessary when important information needs to be conveyed to vehicle or foot traffic to ensure safe passage through a particular area.