Merging is every drivers' nightmare. Numerous studies have shown that the zipper merge is the most efficient way for drivers to merge and ensure less traffic. But is it possible in practice?
There are two kinds of people in the world. those who see that the right lane ends ahead and immediately move into the left lane, and those who keep driving along in the left lane until the last second.
We’ll call those folks late mergers, though if you’re an early merger, you probably have more colorful names for them.
So, you might be surprised to know, the late mergers have been right all along and there’s a scientifically sound reason why we should all start doing it.
The late merge is also called the zipper merge. It’s the most efficient way to funnel a high volume of cars from two lanes into one, according to science. If the zipper merge is so great, how come you’ve either never heard of it, or you get the finger when you do try it?
A bunch of states and cities have tried to spread the word.
Here’s how the Minnesota DOT illustrates zipper merging
This was just part of their publicity campaign for the zipper merge in 2011; they also had billboards and registered the domain dothezippermerge.org.
Kansas DOT joined in a few years later, in 2014:
And here’s the Missouri DOT.
It works because it’s a more efficient use of space--cars are using all available lanes until the choke point.
There are tons of studies that show that If we all used the zipper merge, we’d improve traffic flow and reduce the duration and physical length of backups.
In Germany, they’ve used the zipper merge since the 1970s and it’s the law. Minnesota, Missouri, Kansas, and Washington state officially endorse it, Colorado and Pennsylvania have used it at particular construction sites, Texas and North Carolina are studying it with an eye towards implementing it statewide.
In a traffic simulation or a math equation, the zipper merge might look ideal.
But in the human brain, it looks like cheating. And behavioral studies show that we hate cheaters: when people think someone is getting an unfair advantage, they will go to great lengths to “punish” the cheater.
this plays out on the roads. It explains why people hate late mergers--they perceive them as cutting in line, getting one over on the early-mergers.
When Minnesota did a trial run of the late-merge in 2003, they put up signs like USE BOTH LANES and MERGE HERE. Some drivers were observed acting as vigilante lane-enforcers, weaving in and out of lanes to prevent late-mergers from getting in. Others straight-up ignored the signs and merged early, and the whole thing caused “unnecessary disruptions in the traffic flow.”
That’s partly why California still endorses the early merge--citing last-minute merges as a cause of sudden braking and rear-end collisions that make traffic worse.
And there’s a real, measurable cost to traffic jams.
In 2017, US drivers spent an average of 41 hours sitting in traffic. When you factor in the lost productivity, the wasted fuel, and the higher shipping costs of getting goods through congested areas, the backups cost over $305 billion, which is an average of $1,445 per driver every year.
That’s one reason to look forward to the advent of smarter cars. According to engineers and physicists and the laws of fluid dynamics, traffic flow would be most efficient if every car maintained a consistent speed, and consistent space between the car ahead and the car behind. Smart cars, using sensors to communicate with each other, would be able to maintain optimal speed and distance for us, thereby getting around the problem of human nature.
Until then, the real question to answer is this: can we overcome our lizard-brains, and let that late-merging driver into our lane, for the better good?