Electronic Highway Message Boards: Regulations and Guidelines

Changeable message signs give drivers real-time information, but their content and placement follow rules. Here is how to use them so the message helps rather than confuses.

Changeable message signs, also called CMS or message boards, put words in front of drivers about what lies ahead. That power comes with responsibility, because a poorly worded or badly placed board distracts more than it informs.

Keeping messages readable

• Keep messages short enough to read at highway speed in one or two glances.
• Limit each display to a single idea rather than cramming multiple instructions.
• Avoid abbreviations that drivers cannot decode instantly.

Placement and consistency

A message board works with the rest of the traffic control setup, not against it. Place it far enough ahead that drivers can act on the information, and make sure it agrees with the arrow boards, signs, and lane closures downstream. A board that contradicts the physical setup erodes driver trust in every sign after it.