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Thursday, March 15, 2012

Why Does A Little Bit of Rain Make Our Commute Suck So Much?

Posted By on Thu, Mar 15, 2012 at 3:18 PM

Those who listen to KALW on their way to work in the morning have probably already heard the station's weather guy explain over and over again how it's going to be raining all week. Of course, he says all this before chirpily adding, "And boy do we need it."

But what we don't need is more traffic jams, and that's exactly what this rain is bringing us, aside from soggy sneakers. So those commuters stuck on the Bay Bridge for longer than usual, watching their wipers snap back and forth, probably don't think we need this rain.

Cars packed along I-80 headed west this morning were in stop-and go mode all the way from  Pinole. And yesterday evening, the Bay Bridge commuting crowd, who know traffic better than any other, sat frozen for seconds at a time.

Which brings us to the obvious question: How is it that under 2 inches of rain -- not snow, not floods, and no wind gusts to be felt -- bring Bay Area commuters to such a frustrating stand-still?

Here's how traffic expert John Hourdos, director of the Minnesota Traffic Observatory, explains it to us. Drivers on a highway act as a single organism, each car's movement dependent upon the movement of the cars around it as well as the cars miles ahead of it.

"Anything that happens is because it's a collective decision of all the drivers to drive a certain way," Hourdos says.

While modest rain will barely affect the behavior of individual drivers, these slight effects accumulate, and multiply in magnitude with each car.

"When it rains, you instinctively know that your vehicle will not be able to slow down as quickly as in normal situations," he says. "Instinctively, you leave a little bit more room in front of you. That little room, let's say two feet, if you have 10,000 cars, it becomes a lot of unused space. The same applies with speed. You don't accelerate as fast, you don't select the same speed as you would on a normal day. "

This ripple effect is especially potent in the Bay Area because of the tolls and the numerous sharp curves. "During turns on a wet road, you slow down more than you would slow down on a normal day," says Hourdos. "This effect is progressive backward. Anything that one driver does, it multiplies itself as you go backward."

So next time the asshole in front of you comes to a screeching halt, just know that the bigger asshole is likely a mile or two mile ahead.

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Albert Samaha


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