This guide summarizes the MUTCD requirements and practical application guidance for the W23-1 SLOW TRAFFIC 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.
Used where slow traffic ahead conditions apply on a California project
Advance warning area, ahead of the work.
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.
The W23-1 Slow Traffic Ahead sign is a California MUTCD work zone warning sign. It is shown here as an educational reference with the official FHWA Standard Highway Signs layout and California sizing guidance.
The W23-1 Slow Traffic Ahead sign is a California MUTCD work zone warning sign. It is shown here as an educational reference with the official FHWA Standard Highway Signs layout and California sizing guidance. In the field, W23-1 Slow Traffic Ahead is typically positioned at the advance warning area, ahead of the work. Common deployments include used where slow traffic ahead 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.
Advance warning area, ahead of the work.
Typical minimum: 48" × 48" on conventional roads; 60" × 60" on expressways and freeways.
W23-1 Slow Traffic Ahead 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 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.
Public Ready supports sign selection, project-ready sign packages, and equipment sourcing through qualified providers — with expert support built for compliance.
