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-style sign reference illustration. Always verify against the official CA MUTCD and Caltrans sign charts.
| Sign code | W20-4 |
|---|---|
| Federal code | W20-4 |
| Name | One Lane Road Ahead |
| Category | Warning Signs |
| Shape | Diamond |
| Color | Orange background, black legend |
| California status | Used in California per CA MUTCD |
| Typical CA minimum size | 48" × 48" on conventional roads; 60" × 60" on expressways and freeways |
Download this sign or open the official MUTCD reference.
Official source: FHWA Standard Highway Signs, 2024 (11th Edition) — Warning & Temporary Traffic Control signs.
Source: FHWA Standard Highway Signs — Public Domain. California: CA MUTCD 2026 (effective Jan 18, 2026).
Files linked from FHWA are official government publications in the public domain. CA MUTCD and Caltrans links open official government websites. Always verify against the current edition.
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 two-way traffic will be reduced to a single shared lane ahead, where opposing directions must take turns through the work area. 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.
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.
Common field deployments
Agency review note
StreetsLA, LA County DPW, and Caltrans District 7 may require larger sizes or additional devices. Verify with the reviewing agency before finalizing the TCP.
Typical minimum: 48" × 48" on conventional roads; 60" × 60" on expressways and freeways.
Sizes are CA MUTCD minimums and vary by roadway classification and speed. Verify against the CA MUTCD 2026 (CA MUTCD Part 6 (Temporary Traffic Control), Chapter 6F; warning-sign design in Part 2C), Caltrans sign specifications, and the reviewing agency.
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.
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.
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.
These signs are typically deployed alongside W20-4 on a California TCP.
Setting up alternating one-way control? Public Ready can supply ONE LANE ROAD AHEAD (W20-4) and the supporting flagging signs.
Free official resource — opens official government website
Free official resource — opens official government website
Free official resource — opens official government website
Free official resource — opens official government website
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.
To understand the bigger picture around permits, agency review, lane closures, and pedestrian access for work zones using W20-4 One Lane Road Ahead, visit WorkZoneCompliance.com.
Public Ready can help with W20-4 One Lane Road Ahead — including sign rental or purchase, work-zone signs, TCP sign legends, and permit coordination, and agency-review support for Caltrans District 7, the City of Los Angeles, and LA County.
