ONE LANE ROAD AHEAD Sign Requirements

1. When a ONE LANE ROAD AHEAD Sign Is Used

Warns that two-way traffic will be reduced to a single shared lane ahead, where opposing directions must take turns through the work area.

• 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

2. How and Where It Applies

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.

3. Placement and Application Notes

Position W20-4 advance warning area, ahead of the work.

• Place the sign where drivers have a clear, unobstructed view on approach.
• Mount at the standard height and setback from the edge of the traveled way.
• Do not mount with other signs on the same post unless space constraints require it.

4. Standard Sizes and Visibility Considerations

Typical minimum: 48" × 48" on conventional roads; 60" × 60" on expressways and freeways.

• Choose size based on roadway speed, sight distance, and mounting location.
• Maintain high retroreflectivity for maximum night and adverse-weather visibility.

5. California 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.

6. Common Field or Planning Mistakes

• 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.