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Why Traffic Jams Happen ‘Out of Nowhere’

Picture yourself cruising down a highway with traffic flowing smoothly when all of a sudden the cars ahead of you start to slow down. Within moments, you’re stuck in the midst of a full-blown traffic jam. You inch forward only to discover there is no accident, no construction, and no apparent cause for the congestion. If this situation sounds all too familiar, then you’ve probably already experienced a ‘phantom jam’, but why do they happen? And more importantly, can they be prevented?

Phantom jams

Phantom jams, also called traffic waves or ghost jams, occur out of the blue without any visible explanation for the slowdown. Recent research, however, suggests that one of the main reasons behind these jams is a lack of sufficient spacing between vehicles on the highway. In 2018, CBC interviewed Berthold Horn, Professor of Computer Science and Engineering at Massachusetts Institute of Technology, and he had this to say about it:


“If everyone stopped tailgating, that would already dramatically improve the situation.”


Using complex math models, Horn simulated the scenario and came up with a shockingly simple solution to the problem: Stop tailgating. In fact, he went even further, claiming that if every car on the road maintained an equal distance between the car immediately ahead and behind, it would cut driving time by almost half.


So, just how close is ‘too close’ when it comes to following distance? Generally speaking, drivers should keep a minimum following distance of 3-5 seconds in ideal conditions, and more in adverse conditions. And while it may be tempting to tailgate in an attempt to save time, the risks far outweigh the reward.


In 2021 alone, the number of fatal motor vehicle collisions caused by speeding and aggressive driving increased by 31%. Meanwhile, a recent Leger survey revealed that over half of Canadians have engaged in road rage behaviours like honking, brake-checking and tailgating. So, as temperatures rise and tempers begin to flare, remember that the best way to beat the heat is by giving yourself more than enough time to get where you’re going.

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