Right lane closed ahead! Sign informs drivers in the right lane that they need to merge left to avoid the obstruction. A sign works.
Standard: 01 The Lane(s) Closed sign shall be used in advance of that point where one or more through lanes of a multi-lane roadway are closed. 02 For a single lane closure, the Lane Closed (W20-5) sign shall have the legend RIGHT (LEFT) LANE CLOSED, XX FEET, XX MILES, or AHEAD. Where two adjacent lanes are closed, the W20-5a sign shall have the legend 2 RIGHT (LEFT) LANES CLOSED, XX FEET, XX MILES, or AHEAD.