DETOUR Sign Requirements
This guide summarizes the MUTCD requirements and practical application guidance for the M4-10 DETOUR sign. Use this resource to understand when it is required, how to place it correctly, and how to maintain clear visibility for safe operations.
When It Is Used
Used where detour conditions apply on a California project
Where It Applies
Along the detour route at each decision point.
Placement Basics
Mount at the standard height and setback for the roadway with clear sight lines.
Visibility / Reflectivity
High reflectivity and clear sight lines are essential day and night.
1. When a DETOUR Sign Is Used
The M4-10 Detour sign is a California MUTCD detour sign. It is shown here as an educational reference with the official FHWA Standard Highway Signs layout and California sizing guidance.
- Used where detour conditions apply on a California project
- Selected and sized per the CA MUTCD and the roadway type
- Coordinated with the overall traffic control plan and permit
2. How and Where It Applies
In the field, M4-10 Detour is typically positioned at the along the detour route at each decision point. Common deployments include used where detour conditions apply on a California project; selected and sized per the CA MUTCD and the roadway type; coordinated with the overall traffic control plan and permit. 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 M4-10 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
M4-10 Detour is used in California per the CA MUTCD. Confirm its size, retroreflective sheeting, placement, and spacing against the CA MUTCD 2026 and the reviewing agency before finalizing the traffic control plan.
Go to California Notes6. 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.
Related Resources
View All M-Series Signs
Educational reference only. This is not an official Caltrans, FHWA, or local agency publication and is not legal or engineering advice. Always verify sign selection, size, placement, spacing, and application against the current CA MUTCD 2026, Caltrans sign specifications, Standard Plans, project documents, and the reviewing agency’s requirements. Local jurisdictions may impose additional requirements, and final selection, placement, and dimensions may require engineering judgment or agency approval. Written against California MUTCD 2026 (effective January 18, 2026) and the Federal MUTCD 11th Edition. Official sources last verified June 2026.
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