What Are Message Boards?

A message board, also called a portable changeable message sign, is an electronic sign that can display different messages about closures, detours, or conditions ahead. The message can be updated as conditions change. Because the text is changeable, these boards are useful for communicating information that varies over the course of a project.

Last updated: June 24, 2026

Why It Matters

Message boards can warn drivers in advance of an upcoming closure or detour, giving them time to choose another route. A confusing or outdated message reduces that benefit.

They are often used to prepare drivers before they even reach the advance warning signs.

Where It Shows Up in the Field

Message boards appear upstream of larger closures and detours, including on busy Southern California corridors where advance notice helps spread traffic.

In the field, the board is placed where drivers can read the full message at speed.

Common Mistakes

Displaying a message that is too long to read at speed.
Leaving an outdated message after conditions change.
Placing the board where it is blocked or seen too late.
Using vague wording that does not tell drivers what to do.

What to Check Before Work Begins

That the message is short and clear enough to read at speed.
That it reflects current conditions.
That placement gives drivers time to act.
That the board is consistent with the rest of the setup.

Related Terms

Frequently Asked Questions

What is a portable changeable message sign?

It is a trailer-mounted electronic sign, also called a message board, that can display updatable messages about closures, detours, or conditions ahead.

How long should a message be?

Short enough to read at speed. Long or cluttered messages are hard to absorb, so the wording is kept brief and clear.

Where are message boards placed?

Usually upstream of larger closures and detours, where drivers can read the full message and still choose another route if needed.

Need Project-Specific Support?

Work Zone Compliance provides general educational information about work zone compliance. For project-specific traffic control plan support, permit coordination, or public right-of-way planning in Southern California, visit Public Ready.

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