Portable Changeable Message Signs
A portable changeable message sign displays text that can be updated during a project, which makes it useful for information that changes. This page explains how it is used and what governs it.
Last reviewed: June 24, 2026
What It Is
A portable changeable message sign (PCMS), also called a message board or dynamic message sign, is a trailer-mounted electronic sign that displays updatable messages.
Because the text can be changed, it is useful for information that varies during a project, such as changing closures, detours, or conditions.
How It Is Used
- To announce upcoming closures, detours, or schedule changes in advance.
- To reinforce guidance approaching a work zone, alongside the standard static signs.
- To update the message as the work moves through phases.
Why It Matters
- Updatable messaging keeps information current in a way a fixed sign cannot.
- Clear, timely messages help drivers prepare before they reach the work.
Considerations & Limits
- A message sign supplements, and does not replace, the required static signs and devices.
- Message content, placement, and legibility follow the applicable standard and the approved plan.
- Overloaded or confusing messages reduce the benefit; messages must be readable at speed.
Official Sources
- FHWA MUTCD — National device standards, including changeable message signs.
- California MUTCD (Caltrans) — State device standards.