How to manage what's called a phantom traffic jam

Interstate 380 at Wilson Avenue exit, Sept. 27, 2016 (KCRG-TV9)
Interstate 380 at Wilson Avenue exit, Sept. 27, 2016 (KCRG-TV9)(KCRG)
Published: Nov. 22, 2016 at 10:00 PM CST
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Drive in Iowa and you'll experience it. Traffic moving along and then... brake lights. You look for a cause - but see nothing. Then, as fast as you stopped, you're moving again.

Dr. Daniel McGeehee, director of the National Advanced Driving Simulator at the University of Iowa, says there's a simple explanation for what's called a phantom traffic jam.

"When one car brakes in a big string of traffic, it extends this little braking shock wave through traffic, and by the time it makes its way through a whole string of cars, the traffic at the end of a mile or two miles or five miles begins to slow down."

This simulation shows how that wave moves through traffic. You can see cars moving along at their normal speed, suddenly have to brake, and then be able to move again freely.

All from one car braking.

"It could be a parked car on the road, it could be a person who suddenly brakes for a deer, it could be a police officer on the side of the road. We jam on our brakes for a whole bunch of reasons."

To avoid it, Doctor McGeehee says don't tailgate, don't speed and limit your distractions.

"It's really about paying attention."

Construction. Another commuters nightmare. In heavy traffic - you might get mad at the driver who gets over at the last possible second. But Doctor McGeehee says being "Iowa Nice" and moving over early is actually worse.

"Then everybody starts to pile up at that pinch point. And this is really where people need to drive all the way to the end of that and merge at the very last second. We see these backups sometimes for miles of just one lane."

That's a lot of wasted pavement - so zippering is the answer. That's when cars take turns merging, making traffic move more smoothly. The Minnesota Department of Transportation found the zipper merge can reduce the length of a backup by 40 percent. The hitch is that it works only if everyone participates.

These tricks with a little patience and less braking could leave you thankful for a quicker commute.