Arrow Boards, Message Signs, and Warning Lights
Arrow boards direct traffic to merge, portable changeable message signs communicate conditions, and warning lights draw attention. Used correctly they reinforce the setup; used poorly they confuse or contradict it.
Last reviewed: June 24, 2026
Why It Matters
- These devices carry active instructions; when they conflict with the signs and channelizing on the ground, drivers get mixed messages at exactly the wrong moment.
- A dark arrow board or a message sign left on after the work moves undermines the whole setup.
When It Applies
- Arrow boards where a lane is closed and traffic must merge; message signs to communicate conditions or detours; warning lights to supplement devices where added conspicuity is needed.
Planning Considerations
- Show arrow-board and message-sign locations and modes on the plan, consistent with the closure and merge they support.
- Keep messages short and consistent with the fixed signs; specific legibility and placement requirements come from the applicable MUTCD.
Field Considerations
- Aim and position arrow boards so approaching drivers see them in time, and keep them powered and legible day and night.
- Update or turn off message signs when the condition changes, and remove them when no longer needed.
Inspection Considerations
- Inspectors confirm the arrow board matches the closure, messages are current and legible, and devices are powered.
- Contradictory or outdated messages are common findings.
Common Compliance Failures
- Arrow board pointing the wrong way or dark at night.
- A message sign displaying an outdated or contradictory message.
Upstream Prevention
- Plan device locations and messages to match the setup, and assign responsibility for updating them.
- Include arrow boards and message signs in the daily maintenance and reopening checks.
Related Pages
Relevant Signs on MUTCDSignChart.com
For individual sign codes, meanings, and specifications, see the sister site MUTCDSignChart.com. The signs below link directly to their reference pages:
Official Sources
Frequently Asked Questions
What is an arrow board used for?
An arrow board is a lighted display, usually trailer-mounted, that directs drivers to merge or shift away from a closed lane. It is commonly used for lane closures on higher-speed roads.
What is a portable changeable message sign?
A portable changeable message sign (PCMS) is a trailer-mounted electronic sign with updatable text about closures, detours, or conditions. Because the message can change, it's useful for information that varies during a project. It adds to the required static signs — it doesn't replace them.