The world can be divided into two kinds of drivers: Those that get over into a lane to exit or merge early (lineuppers) and those that zoom by until the last moment (sidezoomers), cutting the line in a sense. The war between lineuppers and sidezoomers is part of what makes driving hell sometimes. It turns out, we're all doing it wrong.


You see this in play whenever there are many cars on the road and a lane is closed, ends soon, or there's a busy exit. Lineuppers (as the The New York Times calls them), dutifully slow down and move over into the appointed lane, taking their places. When sidezoomers zip past those who are lined up and try to sidle in at the front, many lineuppers get angry and refuse to let (those cretins, in their minds) in. Then the second lane gets backed up too and we have on our hands a bottleneck.

Slower Traffic Keep Right explains why this is so inefficient:

A similar situation exists where one of the lanes ends 1000 feet or so after the traffic light. To avoid having to merge after the intersection too many people get in the lane that doesn't end before reaching the traffic light. This is done because there is a perception that it is unfair to go in the lane that ends because you get ahead of everybody. Those who are in the lane that doesn't end are rude and make it hard for the ones who are trying to merge after the light. The result is that for much of the time that the light is green we only have one lane's worth of traffic getting through. This inefficiency results in lots of cars piled up waiting to get though the light. Our emotions tell us that nobody should use the lane that ends but logically this won't work. The reason there are two lanes for a short while after the light is so we can get more people through the intersection while the light is green. It makes more sense to go single file after the intersection rather than before.


The proper thing to do, according to engineers in the New York Times article and other sources, is for everyone to:

Stay calm Slow down a bit "Zipper merge"

In the zipper merge, we take turns getting into the lane and use up all available road real estate:

All cars remain in their lanes, using all the real estate. (On the question of frontage roads and exit-only lanes, the experts waffled; those are arguably part of the real estate, they agreed, but they are meant for a different purpose, and this scenario relies upon everybody buying into the same rules. So no frontage-roading or fake-exit-laning, unless there's a sign specifically instructing otherwise.) People in the narrowing left lanes refrain from shooting ahead, while people in the right through lanes — this is hard to swallow, for those of us inclined toward vigilantism, but crucial — leave big spaces in front of their cars for the merging that is about to commence. We resist the freeze-out-the-sidezoomer urge. We prepare to invite them in.

Before and after (see an animated version on Traffic Waves):


Apparently, this is how ants do it, and you never see ants in traffic jams or screaming obscenities at each other, do you?

The Urge to Merge | The New York Times

Slower Traffic Keep Right

Merging-Lane Traffic Jams: A Simple Cure | Traffic Waves

Photo by Cliffski .