Dave Deslauriers /

Phantom Traffic Jams Explained

When people think of what traffic jams, or what causes traffic jams, some of the most common explanations are things such as accidents, construction, and weather. However, most of us have also experienced traffic jams that seemingly have no rhyme or reason behind them. These phantom traffic jams can often leave drivers befuddled and irritated. In this article, we’ll take a look into some of the reasons for these headaches, and take a look at a few things drivers can do to help avoid causing traffic backups.

Cause #1: The Wide Moving Jam

There are generally three main types of phantom traffic jams that occur. The first is known as the wide moving jam. This type of traffic jam is caused by the varying acceleration and deceleration of vehicles in each lane of the roadway. As vehicles accelerate and decelerate erratically, a wave is created, causing traffic further down the road to eventually come to a stop. Tailgating is a major contributing factor to these types of traffic jams, as drivers without enough room to simply slow down when the vehicle in front of them decelerates are forced to come to a stop, thus setting off a chain reaction. You can see exactly how this type of traffic jam forms in the following animation:

Cause #2: The Butterfly Effect

Another type of phantom traffic jam is referred to as the butterfly effect. This type of traffic jam occurs when a seemingly small disturbance in the normal flow of traffic, such as a vehicle changing lanes, results in a sequence of events that causes everyone to slow down. It generally works like this: As a vehicle is preparing to change lanes, they decelerate, thus causing a backup in their current lane. As they change lanes, the vehicle that is letting them cut in front generally has to slow down to let them into their lane. This causes a second lane of traffic to slow. As this is happening, vehicles from the second lane are going to try to move into a perceived “faster” lane if possible, thus perpetuating the cycle throughout each lane. An example of this type of traffic jam can be seen here:

Cause #3: The Bottleneck

The final type of phantom traffic jam is known as a bottleneck. A bottleneck occurs when a roadway suddenly narrows, such as a 3-lane highway becoming a 2-lane highway. As a result, vehicles are forced to slow down as traffic adjusts to the new pattern. Because of that slowdown, traffic downstream, which may have been traveling smoothly, is forced to decelerate and eventually come to a stop. Bottlenecks are one of the most common types of traffic jams, and can been demonstrated here:

How to Reduce Phantom Traffic Jams

Humans are imperfect creatures. We’re not computers, and therefore don’t always make the most efficient decisions. As such, eliminating phantom traffic jams completely is a nearly impossible undertaking. However, there are some things that you can do to help reduce the chances of causing one.

Maintain a Proper Following Distance – By keeping a proper following distance you decrease your chances of having to brake suddenly should the vehicle in front of you slow down. This helps avoid setting off a chain reaction and creating a traffic wave.

Keep Your Speed Consistent – By keeping your speed as consistent as possible, you’re helping to maintain a proper gap in between vehicles, and thus reducing the chances of creating a traffic jam by erratically accelerating and decelerating.

Only Change Lanes When Necessary – We talked about how small disturbances such as changing lanes can help create a phantom traffic jam. Changing lanes forces your vehicle, as well as those around you to decelerate to accommodate you, thus causing a ripple effect downstream. Try to avoid unnecessary lane changes if possible.


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