DETOUR (RIGHT ARROW) Sign Requirements

1. When a DETOUR (RIGHT ARROW) Sign Is Used

Combines the word DETOUR with a directional arrow to point drivers toward the correct turn along the detour route. The official FHWA designation is M4-9 “Detour”; this site labels the right- and left-arrow orientations as M4-9 (Right Arrow) and M4-9L (Left Arrow) only to distinguish the two directions.

• Decision points and turns along a detour
• Used in sequence with M4-8 DETOUR markers
• Common on local-street detours around closures

2. How and Where It Applies

In the field, M4-9 Detour (Right Arrow) is typically positioned at the along the detour route at each decision point. Common deployments include decision points and turns along a detour; used in sequence with M4-8 DETOUR markers; common on local-street detours around closures. Always confirm its size, retroreflective sheeting, spacing, and placement against the CA MUTCD 2026 and the reviewing agency before finalizing the traffic control plan.

3. Placement and Application Notes

Position M4-9 along the detour route at each decision point.

• Place the sign where drivers have a clear, unobstructed view on approach.
• Mount at the standard height and setback from the edge of the traveled way.
• Do not mount with other signs on the same post unless space constraints require it.

4. Standard Sizes and Visibility Considerations

Typical minimum: 24" × 12" (route marker / plaque).

• Choose size based on roadway speed, sight distance, and mounting location.
• Maintain high retroreflectivity for maximum night and adverse-weather visibility.

5. California Notes

Placed at detour decision points in California to direct each turn, keeping detoured traffic on the approved alternate route.

6. Common Field or Planning Mistakes

• Detour not signed continuously at every decision point.
• Arrow direction incorrect at a turn.
• Detour does not return traffic to the original route.
• Pedestrian detour not addressed where sidewalks are affected.