Merging on the highway can be a fraught task. Most people do it the polite way: merging over into the lane as soon as possible, forming a polite line of people waiting to get off the highway or move out of a closed lane. But there’s always that one jerk who speeds ahead of the line of slowed traffic, merging into the lane at the last second possible and cutting ahead of the entire line of cautious drivers who merged a mile back. While we may resent those drivers, according to HowStuffWorks, this aggressive style of merging is actually the most efficient way to keep traffic moving.
The last-minute system, dubbed the “zipper merge,” suggests that all drivers wait until they’re almost at the fork in the road or start of the closed lane to merge over. Instead of creating a long line of cars at a standstill in the right lane, waiting until the last second maximizes road capacity, since cars are moving in both lanes. It also makes the road safer. Don’t believe it? Watch the principle at work in the animation below.
Traffic studies prove that the zipper merge is the most efficient way to keep a road moving. Instead of one lane of traffic whizzing by while the other lane slows down considerably, both lanes slow down slightly, and overall, the slowdown is more equitable across both lanes. According to the Minnesota Department of Transportation, it can reduce the length of backed up traffic by up to 40 percent.
But that assumes that every driver adopts the zipper merge. Unfortunately, it’s very hard to convince a whole society of drivers to suddenly change their behavior. Even if zipper mergers are technically correct, when the whole rest of the highway is operating under the belief that merging as soon as possible is the correct and polite way to go about dealing with a lane closure, that one guy merging at the last moment just looks like a jerk. The system only works if everyone plays by the same rules.
Some transportation departments have tried to encourage drivers to adopt the practice, putting up signs near road closures that ask people to “merge here,” nudging them to wait just a little longer before they get over.
Merging late may go against our very nature, however. Many people tend to “pre-crastinate,” according to one 2014 psychological study, trying to get a task out of the way as soon as possible even when doing so goes against our best interests. Penn State researchers found that when asked to complete the basic task of carrying buckets from one end of an alley to the other, people were willing to do more work rather than delay completing a basic task until the last second. Many participants opted to pick up a bucket closer to them, even when it meant they would have to carry the bucket farther, rather than waiting to pick up a bucket closer to their end goal.
So, it may be no surprise that the zipper merge hasn’t caught on, at least in the U.S. But at least now you can feel justified being that one last-minute merger.