This guide summarizes the MUTCD requirements and practical application guidance for the M4-9 DETOUR (RIGHT ARROW) sign. Use this resource to understand when it is required, how to place it correctly, and how to maintain clear visibility for safe operations.
Decision points and turns along a detour
Along the detour route at each decision point.
Mount at the standard height and setback for the roadway with clear sight lines.
High reflectivity and clear sight lines are essential day and night.
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.
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. 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.
Along the detour route at each decision point.
Typical minimum: 24" × 12" (route marker / plaque).
Placed at detour decision points in California to direct each turn, keeping detoured traffic on the approved alternate route.
Go to California NotesEducational 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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