Physics of Traffic Jams
Researchers say that a "backward traveling wave" can explain why traffic jams sometimes appear seemingly out of nowhere. Cynthia Graber reports.
SUBSCRIBE TO Science Quickly
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
This holiday season, many of us will take to the roads. Which means many of us are also about to face rather unpleasant traffic jams. The most frustrating ones seem to occur for no reason at all. You’re stuck, positive something catastrophic must have happened up ahead. Then for no apparent reason, the traffic clears.
Now mathematicians from England’s University of Exeter believe they have solved this mystery. They modeled the effect of various highway events, such as a truck slowly pulling out from the merge lane. If the truck’s approach causes the car behind to quickly drop below a certain speed, then the next driver back also hits his or her brakes. This continues in a braking chain that the authors call a backward traveling wave. It could stretch back miles.
So it’s not necessarily the volume of traffic, but rather a sudden interruption in the flow that causes delays. The authors advise drivers to pay attention, and, when necessary, brake gently and slowly. If you suddenly overreact and hit the brakes, you could be causing someone to grimace in frustration in a car many miles away.
—Cynthia Graber
It’s Time to Stand Up for Science
If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.
I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.
If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.
In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.
There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.
