How do Traffic Jams Start?

How do Traffic Jams Start?

It doesn’t get much better than zipping along in the fast lane on a beautiful day with your favorite tunes pumping and no vehicles ahead of you. But as is often the case this little slice of automotive paradise can quickly turn into the ninth circle of Hell.

Like some sort of supernatural force, traffic jams can pop up faster than mildew in a frat house shower stall. Worst of all, the roadway-congestion monster doesn’t care that you’re late for an appointment or rushing to the emergency room because of sudden-onset anaphylaxis.

But how do traffic jams start? Let’s explore the wonders of this frustrating phenomenon.


According to the U.S. Department of Transportation Federal Highway Administration there are six sources of congestion. Like an unholy alliance, these factors can even work together to make a bad situation worse, much worse.40-PercentFirstly, bottlenecks are the largest source of highway snags, accounting for about 40 percent of all congestion. These are places where the roadway narrows or heavy traffic demands lead to backups. 25-PercentOn-road incidents are the second-largest contributor to congestion after bottlenecks. Crashes, stalled vehicles and on-road debris cause about 25 percent of all traffic jams. 15-PercentWatch out for grapefruit-sized hail, high winds, drifting snow or fog! Inclement weather has a huge impact on safe, efficient roadway travel. About 15 percent of all congestion can be blamed on less-than-ideal driving conditions. Isn’t it better to just stay home? 10-PercentConstruction is the next thing on this dastardly list of blood-pressure boosting bothers; it’s everyone’s favorite thing! Is it orange-barrel season in your state? Road construction and highway maintenance account for about 10 percent of all thoroughfare jam-ups. 10-Percent-2Finally, special events and poor signal timing result in a combined 10 percent of roadway blockages. We all know how bad driving can be when a major sports event ends and everyone makes a mad dash to get away from the stadium. Likewise, poorly timed traffic lights result in significant backups as well.

Each of these items is bad enough on its own, but imagine the mayhem that can occur if they cooperate. Trying to pass through a traffic bottleneck with poorly timed lights shortly after a three-car pileup took place during a snowstorm is an exercise in not bludgeoning yourself comatose with a tire iron. Starting your own “home-based business” like some late-night infomercials suggest almost sounds more appealing than commuting through that nightmare.

ONearly half of all congestion is what’s known as “recurring,” meaning it happens nearly every day. Think rush-hour traffic. These issues occur when there are more vehicles trying to use the road than there is capacity to handle them.

But the lion’s share of jam-ups are attributable to non-recurring congestion, things like sports events, poor weather and accidents. Needless to say, recurring traffic jams are much more predictable.


Back to that beautiful summer drive you were taking at the beginning of this story and the massive highway Charlie Foxtrot that ruined your day. A lot of times it seems like interstate jam-ups happen for no good reason, and believe it or not they can even be the fault of just one person. Yes ONE INDIVIDUAL DRIVER.

According to, traffic slowdowns can occur when a section of road is carrying its maximum capacity of vehicles and one driver, for whatever reason, slows down. Sharp braking, unnecessary lane changing or heavy trucks getting in the way are all potential sources of deceleration that can severely impact other motorists.

Phantom-Traffic-JamThe trouble is, when you tap the brakes and reduce your speed folks traveling immediately behind have to slow down as well, and the drivers behind them, and the drivers behind them and so on down the line. In fact according to Eddie Wilson from the University of Bristol in the U.K., one small drop in velocity can affect people up to 50 miles away if the conditions are right!

This essentially forms a shockwave that cascades rearward and can cause major issues for everyone traveling on a particular thoroughfare. If you can believe it, depending on road conditions driving slower can actually be faster. For instance, traveling at a constant 50 miles an hour instead of doing 70, then 30, then stopping all together can actually result in reduced travel times (not to mention less stressful trips) and  better fuel economy!

Traffic jams have a number of different sources. Inclement weather, poor highway design or the actions of one boneheaded driver can ruin things for everyone. Roadway delays are an unfortunate fact of life that every motorist has to grapple with from time to time. Our advice is keep a cool head and for God’s sake don’t hit the brakes for no good reason!

[Source: New Scientist]

Source: Daily Mail

  • Don Falloon

    My experience on my regular commute is the person(s) who fail to add a touch of acceleration when they encounter one of the two raised bridges on the Freeway. When the guy in the econobox who’s already got his foot to the floor just to keep up with traffic meets the hill, his speed is going to fall off, and everyone behind him gets to reap the benefit of testing their braking reaction. Of course, this guy was driving in the (used to be) fast lane…

  • dan

    Sunday Drivers NEED to stay out of the LEFT LANE!

  • Soyntgo4it

    Some slow moron that had a bad day at work, is what caused it. Or the guy that tries to rush home and crashes.

  • Joe Kaminski

    They forgot left lane loiterers and in conjunction with construction they forgot to mention those idiots who ignore all of the warning signs saying “Left lane closed 5 miles ahead, 4 miles ahead, 3 miles ahead, etc.” and sit in that lane until the last possible moment, then they expect people to let them in. Or they force themselves in, causing either an accident or a close call.

  • silvrado

    1. Merging. Humans are not good at it.
    2. Not adequate on and off ramps for traffic entering/exiting the freeway.

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