On The Ant Highway, There's Never A Backup A team of Indian physicists has made a mathematical model that purports to explain why ants don't have traffic jams. NPR's Joe Palca explains as part of his series, Joe's Big Idea.

On The Ant Highway, There's Never A Backup

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Traffic is a fact of modern life. Cars, plus more cars, plus trucks and there you are creeping along wondering why you're not going any faster, but of course you're thankful that you're tuned to your local NPR station. But even the most captive of you might have missed this story in the first time around. It's about ants and why crowded roads don't slow ants down. As part of his project Joe's Big Idea, NPR science correspondent Joe Palca has this ant traffic report.

JOE PALCA, BYLINE: Good morning, everyone. Looks like another no-hassle day on the ant highways. Traffic is moving smoothly on Jungle Route 17 near the split. Ants are traveling at speed coming in on 95 through the savanna, heavy volume but no slowdowns on Parkside Drive near the picnic basket.

Now, you may have noticed something a little surprising about this traffic report - no traffic jams. Physicist Apoorva Nagar at the Indian Institute of Space Science and Technology says it turns out, for the most part, ants don't have traffic jams. Nagar wanted to know why that was and whether human traffic engineers could learn a thing or two from ants about how to avoid jams. I reached Nagar via Skype in his office in Kerala, India. He says there are basically three reasons ants don't jam up when running together in a single direction. Number one, ants don't have egos. They don't show off by zooming past slowpokes.

APOORVA NAGAR: They do not want to overtake each other.

PALCA: No aggressive drivers on an ant highway.

NAGAR: The second thing is that they do not mind a few accidents or collisions.

PALCA: So unless there's a serious pileup, they just keep going. And the third reason?

NAGAR: Ants seem to get more disciplined as the density increases.

PALCA: More discipline means no rubbernecking or distracted driving. Nagar felt this kind of behavior could be explained by something called the Langevin equation, an equation physicists use when describing the movement of liquids or how individual atoms behave in a lattice. I wasn't entirely familiar with the Langevin equation, so I turned to Thomas Donnelly, a physics professor at Harvey Mudd College.

THOMAS DONNELLY: This is basically a reworking of Newton's famous F=MA equation.

PALCA: Oh, yes, of course. Force equals mass times acceleration.

DONNELLY: So it's all Newton, but they're using a sort of special description of the forces, which includes a random component.

PALCA: OK, I think that's as far as I'm going to go in explaining that. But the bottom line is when Nagar made a mathematical model of the ants' traffic patterns using the Langevin equation and compared what his model predicted with what experiments with ants running in a line showed...

NAGAR: And they sort of seemed to fit very well with the experiment.

PALCA: So he wrote up his results, and they will appear in the journal Physical Review E. Nagar is not sure how relevant his model will be for human traffic engineers. After all, he agrees allowing cars to bump into each other at 60 miles an hour may be a nonstarter. Although greater discipline and less ego should help keep traffic flowing smoothly.

There's one other tiny problem. Nagar is a physicist, not an ant man. I've talked with ant researchers who say when the volume of ants is high enough, ants do jam up. But I suppose you could solve that problem by building more ant highways. Joe Palca, NPR News.

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