Traffic congestion’s been increasing for most of the 20th century. And it’s only getting worse. Each year, the average commuter in the U.S. sits in traffic for over 40 hours and … are you ready for this? … wastes $1,400 on gas from idling. Ugh.

Yet, as common as it is, gridlock continues to evoke that age-old existential question: “Why is this happening … to me?!” Sometimes it’s obvious — there’s roadwork or an accident ahead. But in many cases, traffic jams up out of nowhere.

While congestion’s gotten worse, we’ve a far better understanding of its dynamics. And many regions are experiencing a turning point. In fact, Esurance recently analyzed all 50 states to see which ones are making the biggest strides in improving the commuter experience. Check out the surprising results here.

We’ll explore the scientific nitty-gritty of common (and often puzzling) traffic jam conditions — including root causes and driving habits that make them worse. Because sometimes understanding why can offer a bit of ease in the uproar. And it might help us drive a little better too.


To understand the physics of traffic congestion, it’s best to begin with the obvious and common scenario: bottlenecks. That’s when you have too many cars and not enough road.

Traffic’s like a stream

Scientists frequently liken congestion to fluid flow and use words like “upstream” and “downstream.” Dump water down a narrow passage and it’ll clog up or bottleneck. The smaller the funnel and more voluminous the water, the greater the bottleneck.

Highway bottlenecks usually occur when there’s a lane drop off. Then you’ve got, say, 3 lanes’ worth of traffic cramming into 2 lanes worth of highway. How quickly traffic gets backed up — or increases “upstream” — depends on 2 factors:

  1. The number of cars “upstream” trying to travel “downstream.”
  2. The bottleneck’s max capacity.

But this leads us to a more confusing phenomenon: when traffic CRAWLS to a halt without explanation.

Well, there’s always an explanation.

Phantom traffic jams

You’re driving along when you see a thread of red tail lights up ahead. Now you’re inching forward, little by little, for what seems like an eternity. Suddenly, it all clears up, almost like it never happened. What gives?

This is called a “phantom” traffic jam. While cryptic-sounding, it’s usually caused by a car slowing down miles ahead.

One brake light = many more

Say one frustrated driver tries to pass a slower vehicle by forcing their car into the adjacent lane. Now the car in the adjacent lane has to brake, sending a shockwave of brake lights upstream. As it travels backwards along the highway, the wave gets larger and larger. And the slowdown becomes greater and greater. Then you’re left with one giant parking lot.

Researchers at MIT equate these shockwaves to those produced by explosions. Using the equation for “detonation waves,” they’re able to accurately predict the shape and speed of shockwaves in vehicle traffic. But the way in which drivers respond to shockwaves — that is, denser traffic — can either minimize or exacerbate it.

How drivers can improve traffic congestion

Let’s go back to the funnel analogy. Pouring a lot of water too quickly down a funnel will cause a bottleneck. Pouring it slowly, however, dramatically improves water flow.

Same with vehicles responding to dense traffic, which requires a more preventive driving strategy.

Defensive driving — the gridlock antidote

Instead of speeding up before hitting the brakes and contributing to the domino effect of brake lights, it’s better to release the gas ahead of time. Doing so helps maintain space between you and the cars ahead, which cushions the spread of shockwaves. In order to anticipate dense traffic, you have to continually scan the road as far down as the eye can see.

This is an example of defensive driving, which MIT’s study says helps stabilize traffic pressure. But it only works if enough drivers are doing this. Otherwise, the destabilizing effects of aggressive drivers will overthrow the stabilizing pressure of defensive drivers.

While there’s much to be said about the need to renovate highway infrastructure, we the drivers are ultimately the biggest culprit of traffic jams. Which means we can also be the solution.

In other words, we really need to stop tailgating each other, you guys.

Good driving can save you money

In more ways than one too.

For starters, there’s less wear and tear on your vehicle from stopping and going incessantly. By keeping your head on a swivel and easing up on the pedals, you also reduce your chances of getting in an accident.

Plus most insurers offer some form of auto insurance discounts for good driving and staying claims-free. Esurance even has an app that crafts a customized discount based on your driving habits: DriveSense® Mobile. It’s free to download. And it could save you $100 just for enrolling.

Of course, we’re an insurance company after all. So start a quick, free car insurance quote with Esurance. And see how easy insurance can be.

Safe and smart | Car safety


about Evan

From writing content for life coaches to working on indie film press releases, Evan’s motley repertoire has been considerable in the last couple of years. Now he employs his varied aptitude as a content writer for Esurance. He’s also a self-proclaimed polyglot in training with a proclivity for dog-eared books.