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The City of Portland, Oregon

Portland Bureau of Transportation

Phone: 503-823-5185

Fax: 503-823-7576

1120 SW Fifth Ave, Suite 1331, Portland, OR 97204

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Fighting Congestion Like Rice Through a Funnel

Picture this: You're driving down the freeway at a crisp, clean 55 mph when you spot a few break lights ahead.  Naturally, you slow down to 40, 30, 20, and now you're stopped.  Bummer.

But what if you and all your fellow highway travelers knew that the traffic congestion was coming and all of you slowed down a mile before the choke point? You'd just hit the bottleneck 30 seconds later right?

Wrong.  In fact, if everyone slows down far enough before the congestion point the bottleneck might magically disappear.  As KATU explains in this article, vehicles and traffic are like rice moving through a funnel.  Pour the rice really fast and it backs up and overflows, pour the rice slowly and the kernels will pass right through and in less time.

Image: Brent Wojah/Oregonian


In hopes of turning I-5 traffic into free-flowing rice kernels, the Oregon Department of Transportation (ODOT) will be installing variable traffic speed signs in a number of locations in the urban core.  If people driving follow the signs it should help ease congestion, reduce crashes, and shave some time and stress off the morning and evening commutes.  During less congested times the new signs won't operate.   This will be ODOT's second application of variable traffic speed signs; the Washington State Department of Transportation (WSDOT) is doing the same thing for a Seattle stretch of I-5.

It's a great idea that ODOT claims can reduce collisions and increase roadway capacity.  Considering the many costs (not just financial) to expand freeways or institute a congestion pricing project, variable speed limits signs could be a low-cost option that helps save a time, money, and headaches for highway users.