Infographic: What Actually Causes Traffic Jams

You already know this, of course: Traffic is awful. But what actually causes those delays that cause you such grief?

freeway traffic

Ah, traffic. The unfortunate consequence of the glorious machines that allow us to traverse distances our ancestors would’ve thought unimaginable without even breaking a sweat is, of course, that we also have to share the roads affording us these distances with other horrible, terrible people drivers. And you know what that means: Traffic jams. But what actually causes traffic jams?

Handy Infographic


A bit more on the numbers: That 50 percent caused by bottlenecking is not quite as straightforward as its “traffic demand exceeds roadway capacity” tag might make you think. Perhaps you’ve always had the sneaking sensation that it was just one or two bad drivers at fault for that giant bottleneck? Turns out, you’d be kind of right about that. Basically, NPR reports, if just one person has to brake suddenly, that can cause a kind of wave reaction. An MIT computer scientist offered NPR this non-jargony explanation: “People who study this talk about chaotic systems and positive feedback, but the practical consequences are that the amount drivers have to slow down increases the farther back you are from the original incident.” The result is a phantom traffic jam, or a bottleneck. There’s another brilliant animated illustration of how a bottleneck occurs here.

50 percent of traffic jams are caused by bottle-necking.

And of course, you’re probably already all too familiar with the disastrous consequences that bottlenecked traffic can have in terms of accidents, road rage, pollution, even public health—in fact, researchers at the University of Boston and Harvard University’s Public Schools of Health have estimated that by 2030, the economic impacts of congestion could be over $100 billion. The public health impacts might hit $17 billion. And you also are familiar with the statistic that for a married couple, one partner commuting more than 45 minutes makes the couple a whopping 40 percent more likely to divorce?

If there’s any silver lining, it’s that in increasing numbers, people are using public transportation. In fact, according to the American Public Transportation Association, in 2013, Americans took 10.7 billion trips on public transportation—the highest in 57 years. What about you? Are you a public transportation advocate? Do you sit in traffic more often than you’d like? Are you an expert at navigating bottlenecked traffic?