Warning Signs
Diamond-shaped signs that alert drivers to changing conditions ahead, including work zones, flaggers, lane reductions, and merging traffic.
Warning signs give road users advance notice of conditions that may not be obvious, so they can slow down and react safely. In temporary traffic control, warning signs are diamond-shaped with a fluorescent orange background and black legend or symbol, and they make up most of the advance warning area on a California TCP.
The W-series signs below cover the most common work-zone warnings in California: ROAD WORK AHEAD, the lane- and shoulder-closure series, FLAGGER, WORKERS, BE PREPARED TO STOP, and the lane-reduction signs. Correct advance distance for the posted speed is one of the most common plan-review issues with these signs.
Sizes follow the CA MUTCD — typically 48″ × 48″ on conventional roads and 60″ × 60″ on expressways and freeways — but local agencies may require larger signs based on the roadway classification and conditions.
Warns approaching drivers that a work operation is taking place on or near the roadway ahead so they can slow down and stay alert for changing conditions.
Warns drivers that a detour is ahead and that the normal route will be interrupted, prompting them to prepare to follow an alternate path.
Warns that the road ahead is closed and that through travel will not be possible, giving drivers time to turn or follow a detour before reaching the closure.
Warns that two-way traffic will be reduced to a single shared lane ahead, where opposing directions must take turns through the work area.
Warns that a travel lane is closed ahead and that drivers in that lane will need to merge into an adjacent open lane before the work area.
Warns specifically that the right-hand travel lane is closed ahead so traffic in that lane can merge left in advance of the closure.
Warns specifically that the left-hand travel lane is closed ahead so traffic in that lane can merge right in advance of the closure.
Uses a flagger symbol to warn drivers that a flagger is controlling traffic ahead and that they must be prepared to stop or follow the flagger's directions.
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.
Warns drivers that they may have to stop ahead, giving advance notice of a flagging station, queue, or signal that can require stopping.
Uses a symbol to warn that a travel lane is ending and that traffic must merge in the indicated direction where the roadway narrows.
A word-message warning that a travel lane is ending ahead, telling drivers the number of through lanes will be reduced.
The California application of the ROAD WORK AHEAD warning, reflecting CA MUTCD and Caltrans conventions for legend, size, and fluorescent orange sheeting in work zones.
The California application of the Flagger warning sign, reflecting CA MUTCD and Caltrans flagging practice, sizing, and fluorescent orange sheeting.
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.
Frequently Asked Questions
Why are work-zone warning signs orange instead of yellow?
Permanent warning signs use a yellow background, but in a temporary traffic control zone the same warnings are shown on a fluorescent orange background to distinguish work-zone conditions. The shape (diamond) and black legend stay the same.
What size is a ROAD WORK AHEAD sign in California?
The CA MUTCD minimum is typically 48″ × 48″ on conventional roads and 60″ × 60″ on expressways and freeways. The correct size depends on the roadway classification — confirm against the CA MUTCD and the reviewing agency.
Is the W20-7 Flagger sign a symbol or a word message?
W20-7 is the flagger symbol sign (a flagger figure). A separate word-message version exists, but the symbol sign is the standard advance warning placed ahead of a flagging station, usually with BE PREPARED TO STOP.
Which warning signs are used for a lane closure?
Lane closures commonly use the W20-5 series (LANE CLOSED AHEAD, RIGHT/LEFT LANE CLOSED AHEAD) for the advance warning, with W4-2 (lane-ends merge symbol) or W9-2 (LANE ENDS) reinforcing the merge at the taper.
Need warning signs for a California work zone?
Public Ready can help you rent or purchase the orange warning signs used in California temporary traffic control and fit them to your TCP.
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