Roads go from three lanes to two lanes or two lanes to one lane all the time – it’s called a “lane drop”.
The wrong way to handle this is to drive until the very end of the lane that’s ending, and then try to merge at the last possible moment, sometimes leading to wrecks like in this video below.
The “LANE ENDS MERGE RIGHT” sign is there to indicate what’s known as a lane drop. Where there were previously two forward lanes of travel, there will soon be only one. Past a given point, cars may not proceed side-by-side, and must order themselves single-file on the narrow road ahead.
At the pinch point, things can get awkward fast. Legally speaking, cars in the left lane NEED to move over, but thanks to right-of-way, no one NEEDS to let them in. To avoid this sticky situation, most drivers will get into The Lane That Does Not End as early as they can.
So who has the right of way, the car on the left or the car where the lane will be ending?
The vehicle that continues straight (not merging) would have the right of way. The driver of the vehicle traveling in the lane that is ending, shall yield to the vehicles in the other lane and only proceed when safe to merge into the continuing lane of travel.