W20-4 One Lane Road Ahead
Warns that two-way traffic will be reduced to a single shared lane ahead, where opposing directions must take turns through the work area.
- Sign Name
- One Lane Road Ahead
- General Meaning
- Warns that two-way traffic will be reduced to a single shared lane ahead, where opposing directions must take turns through the work area.
- MUTCD Code
- W20-4
- Official designation
- One Lane Road (with distance) — FHWA SHS 2024, App. B5-26
- Typical Use
- Advance warning area, ahead of the work.
- Sign Category
- Warning Signs
Specifications
- Standard Shape
- Diamond
- Background Color
- Orange
- Legend / Symbol
- Black legend
- Border
- Black
- Reflectivity
- High Intensity (for nighttime visibility)
- Compliance
- MUTCD / CA MUTCD
Standard Sizes (inches)
- 30 in Diamond30" × 30"
- 36 in Diamond36" × 36"
- 48 in Diamond48" × 48"
- 60 in Diamond60" × 60"
Material / Application Notes
Alternating one-way traffic control through a work zone. Confirm placement and supplemental plaques against the applicable CA MUTCD standard.
View this sign on the Federal MUTCD (FHWA)California Notes
California-specific application notes and adoptions may differ. Review California requirements where applicable.
What It Means / When This Sign Is Used
In the field, W20-4 One Lane Road Ahead is typically positioned at the advance warning area, ahead of the work. Common deployments include alternating one-way traffic control through a work zone; paired with W20-7 Flagger and BE PREPARED TO STOP; common on rural two-lane roads and bridge or culvert work. Always confirm its size, retroreflective sheeting, spacing, and placement against the CA MUTCD 2026 and the reviewing agency before finalizing the traffic control plan.
Learn more about One Lane Road Ahead sign requirementsWhen & Where It's Used
- Alternating one-way traffic control through a work zone
- Paired with W20-7 Flagger and BE PREPARED TO STOP
- Common on rural two-lane roads and bridge or culvert work
Placement on a Traffic Control Plan
- Where it sits
- Advance warning area, ahead of the work.
- CA MUTCD reference
- CA MUTCD Part 6 (Temporary Traffic Control), Chapter 6F; warning-sign design in Part 2C
- Typical minimum size
- 48" × 48" on conventional roads; 60" × 60" on expressways and freeways
California / Field Use Notes
Used where a California work zone narrows the roadway to one lane for alternating one-way control, typically managed by flaggers, a pilot car, or temporary signals.
In Los Angeles, this sign must conform to CA MUTCD 2026. Work in City of LA right-of-way is reviewed by StreetsLA and the Bureau of Engineering (BOE); state highways in LA County are permitted and reviewed by Caltrans District 7; county roads are permitted by LA County DPW. Sizes, retroreflectivity, and placement must meet CA MUTCD minimums — local agencies may require larger signs based on roadway class, speed, pedestrian volume, and proximity to schools or transit.
Common Plan Review Comments
- Sign not shown at the correct advance distance for the posted speed.
- Advance warning sign missing or out of sequence on the TCP.
- Wrong size specified for the roadway classification (conventional vs. expressway).
- Sign sheeting / retroreflectivity class not noted on the plan.
Verify the one-lane section has a defined control method and adequate sight distance for alternating traffic. Public Ready reviews flagging and pilot-car setups.
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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. 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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