BE PREPARED TO STOP Sign (W3-4): What It Means

BE PREPARED TO STOP (W3-4). Illustration drawn by Safe Pass Traffic; not to scale.

The BE PREPARED TO STOP sign (W3-4) warns that traffic ahead may be stopped or backed up. In a California work zone it usually means a flagger, a one-lane section or a queue is coming, so slow down and leave room to stop smoothly.

What it means

W3-4 is a warning sign from the MUTCD’s general warning-sign series (Part 2C). It is not a STOP sign and does not require you to stop at the sign. It tells you that you may need to stop somewhere ahead, often with little notice. In temporary traffic control zones it is used in conjunction with flagger signs and where stops or queues are likely.

Section 6H.15 of the California MUTCD 2026 Edition says the Flagger (W20-7) sign may be used with other warning signs, such as BE PREPARED TO STOP. Section 6L.02 adds that when an Automated Flagger Assistance Device (AFAD) is used, the advance warning signing should include ROAD WORK AHEAD (W20-1), ONE LANE ROAD (W20-4) and BE PREPARED TO STOP (W3-4).

What drivers often get wrong

Waiting to see the stop before slowing. The point of the sign is to give you time. Queues in work zones can end around a curve or over a hill, where you cannot see them until late.
Thinking it is optional because traffic is moving. Flaggers and automated devices switch between STOP and SLOW. Traffic that is moving now may be stopped when you arrive.
Confusing it with a regulatory sign. The orange diamond is a warning. The actual stop instruction comes from the flagger’s STOP paddle, an AFAD, or a temporary signal.
Following too closely in the queue. Leave space. Sudden stops at the back of a work-zone queue are a common rear-end risk.

Where it goes in a work zone

BE PREPARED TO STOP sits in the advance warning area, as part of a series of signs. Under Section 6H.02, where multiple advance warning signs are needed, ROAD WORK AHEAD (W20-1) should be the first one drivers encounter, and sign distances vary with road type, conditions and speed. On a flagging layout, a common sequence is ROAD WORK AHEAD, then ONE LANE ROAD, then BE PREPARED TO STOP, then the Flagger sign closest to the flagger station. The exact placement and spacing are set by the approved traffic control plan, and the permitting agency may require additional signs where queues are expected to extend back.

What contractors need to know

Include W3-4 on the plan wherever flaggers or AFADs will stop traffic, and anywhere the work is likely to create stops or queues.
Think about where the back of the queue will actually be during peak hours. If it can reach past the advance signs, raise it with your plan designer and the permitting agency.
When an AFAD is not in use, the signs associated with it, including those in advance, shall be removed or covered (Section 6L.02).
Keep sign sequence consistent across each approach so drivers see the same message pattern from every direction.

Related signs

Frequently asked questions

Do I have to stop at a BE PREPARED TO STOP sign?

No. It is a warning sign. You must be ready to stop ahead, for a flagger, an AFAD, a signal or stopped traffic, and adjust your speed so you can do so safely.

Is BE PREPARED TO STOP only used in work zones?

No. W3-4 is a general warning sign described in Part 2C of the MUTCD. In work zones, Part 6 uses it with flagger signs and where stops or queues are likely.

Is W3-4 required with every Flagger sign?

Section 6H.15 presents it as an option alongside the Flagger sign, while the AFAD guidance in Section 6L.02 lists it as part of the recommended advance signing. The permitting agency and the approved plan decide what is required on your project.

Sources

Need this sign on a traffic control plan?

Safe Pass Traffic prepares PE & TE stamped traffic control plans, striping plans and typical plans for projects statewide in California, and helps with the permit submittal. We draw the plan that shows which signs go where; your contractor or traffic control provider sets them in the field. Call or text (714) 362-1348 or request a quote.