MUTCD W1-4: Reverse Curve Signs

The W1-4 sign is covered in Section 6H.30 of the Manual on Uniform Traffic Control Devices, 11th Edition. Below are the provisions from that section that describe when the sign is used and how it is placed.

What it means and when it is used

• Guidance · Recommended (should)
  In order to give road users advance notice of a lane shift, a Reverse Curve (W1-4, W1-4b, or W1-4c) sign (see Figure 6H-1 ) should be used when a lane (or lanes) is being shifted to the left or right. If the design speed of the curves is 30 mph or less, a Reverse Turn (W1-3) sign should be used.
• Standard · Required (shall)
  If a Reverse Curve (or Turn) sign is used, the direction of the reverse curve (or turn) shall be appropriately illustrated. Except as provided in Paragraph 3 of this Section, the number of lanes illustrated on the sign shall be the same as the number of through lanes available to road users.

Where to read the rest

• Full text: MUTCD Section 6H.30: Reverse Curve Signs
• Mounting height, lateral offset and retroreflectivity for any sign: MUTCD sign placement guide