zipper merge
n. A merge where drivers use both lanes all the way to the merge point, and then take turns merging.
zipper v.

Example Citations:
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

"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

Earliest Citation:
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

Reader Kelvin Lerch passed along the following via email:

I coined this term, in this usage, in the late '60s, when I was stationed in Washington, DC. There was a particular interchange there, which the traffic reporters referred to as "The Mixmaster", where traffic from two different directions crossed in a single, long "X". In my head, I referred to the actual exchange of traffic as a "zipper". I also used this term to describe the action to my friends back home in California. Unfortunately, I am not a published writer, and the ARPAnet had only just been created, so the ability for an individual to have worldwide publication was decades away.

I have continued to think of long merges (whether between two freeways or simply an onramp) as "zipper merges".

It was interesting to see this term reach acceptability, with an "Earliest Citation" coming 30 years after I coined it!

A zipper merge is not to be confused with a zipper lane, a lane defined by moveable barriers that enable the lane to accept traffic driving in different directions, depending on the time of day. A zipper lane is an example of a contraflow lane.

Right: Example of Zipper Lane in Dallas from Chris Romer on Vimeo.

Here's an earlier cite that uses the form zippering:

I just got back from Holland, where I learned about a new concept in the management of traffic flow: "zippering."

When two lanes have to merge in traffic congestion, the Dutch have disciplined themselves to this simple and courteous system of letting one car proceed from the left lane, then a car from the right lane, then one from the left lane again, like the teeth of a zipper smoothly progressing.
—Jenny Leach, "Let's zip away traffic woes," The Toronto Star, April 20, 1997

Here's another that refers to zipper-type merging and zipper driving:

Doesn't it frost you when you're driving in a construction zone and, being a law-abiding soul, you pull over because one lane will be closed ahead? Then, before you know it, any number of jerks are racing their cars along the inside lane or berm to the last point where they can merge and demand to be let in. Naturally, this clogs traffic and everyone suffers. What to do? ...

State Rep. Ross Boggs Jr., D-Andover, has a better idea. He has introduced a bill in the Ohio House that would force what he calls 'zipper' type merging far ahead of construction zones.
—"'Zipper' driving," Columbus Dispatch, March 22, 1996

Finally, here's the earliest citation I could find that uses zipper to refer to this kind of merge:

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 1, 1977

Related Words: