zipper merge
n. A merge where drivers use both lanes all the way to the merge point, and then take turns merging.
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"And next we can urge drivers to "zipper" when they merge, with some waiting till the last moment to move out of the ending lane. It's a more efficient use of pavement, but it drives early mergers like me crazy."

No, no, no, no, no.

It's the early mergers that screw things up. The "zipper" merge works best when everyone waits until the merge point.
—John Kelly, “John Kelly's Washington: Washington Music, Poker Dreams, Honoring Vets, More,” The Washington Post, July 10, 2009
After passing dozens of cars, I made it to the bottleneck point, where, filled with newfound swagger, I took my rightful turn in the small alternating "zipper" merge that had formed. I merged, and it was clear asphalt ahead.
—Tom Vanderbilt, “Traffic,” Knopf, July 29, 2008
1999 (earliest)
Changes to Tasmanian road rules which align it with the rest of the country, such as the "zipper" merging rule, are also effective from 30 November.
—Danny Rose, “Speed fines increase tonight,” The Mercury, November 30, 1999
Vehicles move through interchange merging areas in a manner similar to a zipper.
—James E. Bernard, An Overview of Simulation in Highway Transportation, Society for Computer Simulation, June 01, 1977
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