The zipper method, in which drivers merge late, is based on the idea of a zipper’s “teeth.” Just as a zipper smoothly comes together, a zipper merge can keep traffic flowing in both lanes by bringing some organization to the merging process, AAA says.

“The zipper merge has shown to keep traffic moving more smoothly, compared to a less structured approach,” Van Tassel said.

A zipper merge is recommended because leaving a lane unoccupied as a result of early merging is inefficient. It only makes traffic heavier, proponents say.