W21 Series — Workers and Equipment Warning Signs
Warning Signs · CA MUTCD Part 6, Chapter 6F
The W21 Series includes warning signs that alert drivers to workers, equipment operators, and utility crews in or near the traveled way. These orange diamond signs are used wherever workers are exposed to traffic — at active excavation, equipment staging, utility operations, and shoulder maintenance. WORKERS (W21-1), SHOULDER WORK (W21-5), SHOULDER CLOSED (W21-5a), and UTILITY WORK AHEAD (W21-7) are commonly combined with the W20 Series advance warning to give drivers adequate advance notice of human presence near the roadway.
California Field Use Notes
W21 signs must be placed far enough in advance that drivers have time to slow before reaching workers. Reviewers often flag W21 signs placed at the activity area instead of in the advance warning area. When workers are on foot near live traffic, WORKERS (W21-1) is posted in the advance warning area upstream of the activity. For shoulder operations, SHOULDER WORK (W21-5) or SHOULDER CLOSED (W21-5a) is used to alert drivers that the shoulder is occupied.
Showing 11 of 11 signs
Uses a worker symbol to warn that workers are present on or near the roadway ahead, signaling drivers to reduce speed and increase caution.
Warns that work is taking place on the shoulder ahead, alerting drivers to workers and equipment near the edge of the traveled way.
Warns that the shoulder is closed ahead and is not available for stopping, disabled vehicles, or travel through the work area.
Warns that utility work is taking place on or near the roadway ahead, alerting drivers to utility crews, equipment, and possible lane or shoulder impacts.
The W21-1a Workers 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 W21-2 Fresh Oil 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 W21-3 Road Machinery 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 W21-4 Slow Moving Vehicle 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 W21-5b Shoulder Closed (with distance) 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 W21-6 Survey Crew 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 W21-8 Mowing 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.
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.
Need W21 Series signs for a California project?
Public Ready can help you source, rent, or purchase W21 Series signs and integrate them into a compliant traffic control plan. For work zone compliance support, visit WorkZoneCompliance.com.