Wonder Why Wednesday: Network Overload

Picture this…

You are cruising down the freeway, minding your own business and rocking out to the latest Taylor Swift song. Just a nice, casual drive to the mall. Everything is going great until you notice some traffic up ahead.

“Uh oh,” you think, “there must be an accident.”

Five Taylor Swift songs later, you are still inching along through the traffic. This accident must be big.

All of a sudden, cars start to move. Poof! The traffic jam is over. But wait. There was no major accident. No police cars. Not even a fender-bender.

“What? How could that happen?” you ask T-Swift. She just tells you to shake it off.

But you can’t just shake it off. You want answers! What the heck just happened? How was there no accident? What caused that traffic?

Well, you’ve come to the right place. I will answer those questions and more in today’s edition of Wonder Why Wednesday.

Why is There Traffic When There’s No Accident?

Has the above scenario happened to you? I’m guessing it has. According to The Atlantic, Americans spend 38 hours a year stuck in traffic. With all that time spent in traffic, we are bound to run into a few instances where the traffic appears to have no cause.

But actually, the cause is quite easy to explain.

To answer this question, a Japanese research group set up circular track with a circumference of 230m. They put 22 cars on the road and asked the drivers to go steadily at 30km/h around the track. Initially, there were no problems. But as soon as a driver altered his speed, things changed and led to brief standstills.

Yuki Sugiyama, physicist from Nagoya University, said, “Although the emerging jam in our experiment is small, its behavior is not different from large ones on highways. When a large number of vehicles, beyond the road capacity, are successively injected into the road, the density exceeds the critical value and the free flow state becomes unstable.”

So basically, traffic jams that are not caused by accidents are simply the result of there being too many cars on the road. calls these types traffic jams, “network overload.” They echo the findings of the Japanese researchers and explain that it boils down to demand outweighing capacity. Just as your computer slows down when you have too many programs open at once, highways and roads are slowed down because of too many drivers.

The site breaks down the occurrences of traffic in two areas: network overload and traffic disturbances.

Traffic disturbances are the accidents, collisions, and breakdowns. According to the 2007 Urban Mobility Report from the Texas Transportation Institute, this type of traffic accounts for between 52 and 58 percent of the delays motorists experience

So the other 42 to 48 percent, or roughly 17 hours of the year you spend in traffic is caused by network overload.

17 hours of year sitting in phantom traffic. That is a lot of Taylor Swift songs to listen to. Don’t worry. Shake it off.



Photo credit: Wikipedia