ATLANTA – Traffic jams are a way of life in Atlanta, and commuters are constantly baffled by congestion that has no apparent cause.
It’s probably happened to you. On a random Saturday afternoon traffic comes to a standstill. There are no accidents. There’s no construction.
Why does it happen?
Traffic engineers call it a “phantom” traffic jam. A single driver can make it happen.
Georgia Tech Professor Jorge Laval tells 11Alive’s Why Guy that something as simple as sunshine can cause a driver to slow just a bit. The next driver in traffic hits his brakes. The driver behind him isn’t paying close attention and has to hit the brakes a little harder.
It starts a wave of brake lights that can travel backward for miles.
“The wave of brake lights travels backward at a consistent 15-miles-per-hour,” says Laval. “Drivers changing lanes to get around the jam causes the wave to travel sideways.”
Laval says drivers hitting an incline of as little as 3% cause traffic to slow enough to cause a phantom jam.
“Twenty minutes later you can have someone in the back of the pack still experiencing the ripple effect,” says Natalie Dale of the Georgia Department of Transportation.
Dale says inattentive drivers are a big part of the problem. They’re the ones surprised by the traffic slowing in front of them and cause panic in the drivers behind them when they slam on their brakes.
