DETOUR AHEAD Sign Requirements
This guide summarizes the MUTCD requirements and practical application guidance for the W20-2 DETOUR AHEAD 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
Advance warning ahead of a full road closure with a signed detour
Where It Applies
Advance warning area, ahead of the work.
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 AHEAD Sign Is Used
Warns drivers that a detour is ahead and that the normal route will be interrupted, prompting them to prepare to follow an alternate path.
- Advance warning ahead of a full road closure with a signed detour
- Used with M4-8/M4-9 detour markers and directional arrows
- Common on local street closures requiring a marked alternate route
2. How and Where It Applies
In the field, W20-2 Detour Ahead is typically positioned at the advance warning area, ahead of the work. Common deployments include advance warning ahead of a full road closure with a signed detour; used with M4-8/M4-9 detour markers and directional arrows; common on local street closures requiring a marked alternate route. 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 W20-2 advance warning area, ahead of the work.
- 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: 48" × 48" on conventional roads; 60" × 60" on expressways and freeways.
- Choose size based on roadway speed, sight distance, and mounting location.
- Maintain high retroreflectivity for maximum night and adverse-weather visibility.
5. California Notes
Used in advance of a detour in a California TTC zone, ahead of the DETOUR route markers that guide traffic along the approved alternate route.
Go to California Notes6. Common Field or Planning Mistakes
- Sign not shown at the correct advance distance for the posted speed.
- Advance warning sign missing or out of sequence on the TCP.
- Wrong size specified for the roadway classification (conventional vs. expressway).
- Sign sheeting / retroreflectivity class not noted on the plan.
Related Resources
View All W-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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