M4-9 DETOUR (RIGHT ARROW) Requirements
Application notes for M4-9 DETOUR (RIGHT ARROW). The official manual distinguishes mandatory standards, recommended guidance, and optional applications; consult the linked sources for the provisions that apply.
1. When DETOUR (RIGHT ARROW) 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. Placement and Application Notes
Position M4-9 at the detour decision point or route assembly identified by the design.
- Place the sign where the intended road users have a clear, unobstructed view on approach.
- Use the mounting height and lateral placement specified for the sign and installation type.
- Use sign assemblies and supplemental plaques only as provided in the applicable manual and approved design.
3. Layout Sizes and Visibility Considerations
Linked-layout dimensions: 30" × 24"; 48" × 36". Check the applicable MUTCD and agency requirements for the required installation size.
- Choose size based on roadway speed, sight distance, and mounting location.
- Use the visibility and material requirements specified for this sign and installation.
4. Sign Selection Checks
- Match M4-9 and its displayed legend to the intended condition.
- Check the source drawing for the required directional or message variant.
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Verify M4-9 Requirements
This is an educational reference. Verify sign use, size, placement, and application against the current CA MUTCD, Caltrans sign specifications, Standard Plans, and the reviewing agency. Official source links are gathered in one place.
View official sourcesEducational 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. Reference editions: California MUTCD 2026 (effective January 18, 2026) and the Federal MUTCD 11th Edition with Revision 1.
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