What causes those ‘unexplainable’ traffic jams?

CHICAGO (NEXSTAR) – Traffic jams are nearly unavoidable on highways and interstates. Sometimes it’s easy to explain — crashes, construction, and sudden influxes of cars, for example. 

Americans are spending more time stuck in traffic than in recent years. Data and analytics firm INRIX recently released its Global Traffic Scorecard, showing plenty of U.S. cities are among the most congested. 

Nationally, the study found U.S. drivers “lost” an average of 51 hours sitting in traffic in 2022. Drivers in Chicago lost more hours – 155 – than drivers in any other metro, according to INRIX. 

When there is no obvious reason causing traffic delays, it can be a bit more infuriating.

The phenomenon does have a name: phantom jam. 

It starts when one vehicle on an already busy roadway slows, even slightly, Berthold Horn, a computer science professor with the Massachusetts Institute of Technology told LiveScience in 2018. 

Temple University mathematician Benjamin Seibold told Vox the same thing, explaining that it could be the smallest interruption that starts a wave of traffic. Those traveling waves were dubbed “jamiton” by Seibold and a group of researchers from MIT, McGill University, the University of Alberta, and KAUST.

Researchers say that jamitons “rarely stay alone” and can occur multiple times throughout long stretches of traffic. 

“The instabilities are observed to grow into traveling waves, which are local peaks of high traffic density, although the average traffic density is still moderate (the highway is not fully congested),” the researchers wrote. “Vehicles are forced to brake when they run into such waves. In analogy to other traveling waves, so called solitons, we call such traveling traffic waves jamitons.”

It might be easy to blame a single car, but more likely, it’s the overall driving behavior of everyone on the roadway. Slowing down just slightly can cause everyone behind you to do just the same. Driving as fast as possible only to brake at the last minute isn’t any better, Seibold explained.

So how can you avoid being the cause of a phantom jam and subsequent jamiton?

Tom Vanderbilt, who wrote a book about traffic (appropriately titled, Traffic), explained congestion and how to avoid it at a conference in 2013, according to Bloomberg. In addition to using the zipper merge, which some states don’t recommend, Vanderbilt recommends maintaining a steady speed and distance from the car in front of you. 

Both Vanderbilt and the aforementioned researchers suggested self-driving cars or electronic driving assistance could help motorists drive more smoothly in traffic, which could make jamitons less frequent.

Guidance from the National Highway Traffic Safety Administration says you should be 3 or 4 seconds behind the motorist ahead of you. Similarly, Horn recommended to NPR that you should try to stay halfway between the car ahead of you and the car behind you.

You can also try to cut down on highway congestion overall. Vanderbilt suggests using public transit, for example, while AAA recommends carpooling.

Michael Bartiromo and WHTM’s James Wesser contributed to this report.

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