Summer is long gone, meaning that nearly all of us have returned to our daily freeway commutes, which are often full of clogged construction zones. Want a tip to make the drive go faster? Use the "zipper merge" whenever possible.
The funny thing about the zipper merge (aka "the late merge") is that it seems to encourage bad behavior. It runs counter to much of what we've been taught by parents, peers, and even driving instructors.
Law-abiding motorists typically think that as soon as they see signs indicating a merge ahead, they ought to shift to the appropriate travel lane. And so, we dutifully tap our turn signals, check our blind spots, and migrate left or right, where invariably things grind to a halt.
We see other drivers still zipping along in the lane we've left behind, wondering if they didn't see the merge warnings or if they're just being jerks. Either way, we have a tendency to sneer, happy to know that we're not "that guy" or "that girl".
But whether they're just trying to get a few cars ahead or whether they actually know how these things works, that guy and that girl are doing it right. That's not just our opinion, it's the opinion of many traffic control agencies and police departments, too--though notably, California refuses to believe it.
Here's the problem: when everyone merges at the same time, it slows traffic to a crawl. When one person in the line brakes, the effects ripple backward, causing trouble. (For a great demonstration of how this "shockwave" effect works, check out the video below.)
However, when drivers zipper merge at the point where lanes converge, it keeps traffic in two separate lanes as long as possible. That keeps cars moving more smoothly--though if zipper-merging motorists aren't careful and courteous, they can cause excessive braking in the other lane, which minimizes the benefits.
Some cities and states have actively begun to encourage zipper merging in construction zones and other areas. If that's the case where you live, let us know how things are going in the comments below.