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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883


When to merge

When two lanes of traffic going the same direction narrow to a single lane, the question of when to merge arises.  And whenever that question arises, divergent opinions emerge.

For some, their “common sense” tells them to move out of the soon-to-be-closed lane as soon as they see the signs warning of the narrowing ahead.  But others reason that both lanes should be utilized up to the merge point, where they expect to be “let in.”

A Fort Collins, Colorado traffic engineer, Joe Olsen, opined, “We all learned in kindergarten not to cut in line, and there are lots of people who think zipper merging is cutting in line.” With credible scientific merit, he added, “Zipper merging is for the greater good, but people still don't see it that way.”

Many studies have suggested that zipper merging, where drivers continue using both lanes up until the actual merge point, then engage in an orderly zipper-tooth-like blending, as vehicles from the closed lane seamlessly, one-by-one, fill spaces left between vehicles in the open lane.

Instead, when drivers put this science-backed approach to the test, they are met with horn honks, single-finger salutes and outright vehicle-blocking.  I’ve seen that latter one performed by truckers who evidently bristle at the efficiency-proven attempt by pulling to the closed lane early in the backup to keep vehicles out of the lane that will eventually be closed.

That resistance and show of ire toward the zipper theory is a shame — especially since that method of merging is recommended, based on research by many states and the American Automobile Association.  William Van Tassel, AAA Manager of Driver Training Programs said, “The zipper merge has shown to keep traffic moving more smoothly, compared to a less structured approach.” 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 according to AAA studies.

A zipper merge is recommended by proponents because leaving a lane unoccupied as a result of early merging is inefficient.  The Colorado Department of Transportation encourages drivers to use the zipper tactic, saying it can reduce delays up to 40 %.  The Minnesota DOT actually ran a campaign promoting the zipper-effect during this decade — complete with billboards.

So do I buy all of that? Yes. Do I practice the zipper? No.  I retreat fairly early to the open lane reluctantly joining the long lineup that will eventually let in the late mergers passing us by.  I succumb to the less controversial early-lineup to avoid arousing road rage.

Most states lack a stance on lane-closure merging.  When asked what behavior is best in such scenarios, one California Highway Patrol spokesperson advised that drivers should merge cordially and safely.  I like that approach, since its adherence precludes conflict. 

I fear, however, that cordial merges inevitably devolve into potential mayhem as soon as the first driver attempts to drive past a long line of vehicles up to the actual merge point.  That driver may be doing the right thing in the interest of traffic flow, but those efforts will likely be discouraged or physically thwarted by someone in the line of stopped cars and trucks.

However it’s handled, it’s important to remember that the merging process should not be considered a competition or race.  “When merging, your goal should be to maximize your smooth ‘flow’ forward through traffic, not to ‘beat’ other drivers," reminds AAA’s Van Tassel.

Readers may contact Bill Love via e-mail at