Kicking hybrids out of carpool lanes slows down traffic


So maybe you think the nuts, bolts, ebb, and flow of traffic congestion are irreversible forces of nature. If so, you probably don't study civil engineering at UC Berkeley or have Dr. Michael Cassidy as a professor.

Fact: traffic flows can be modeled by mathematics, and numbers don't lie.

"If one can understand the nature of congestion and how to combat it, the world is a better place," says Cassidy.

So when California expelled hybrid vehicles from the carpool lanes to keep them from becoming overcrowded, Cassidy looked at a stretch of Highway 880 in Hayward.

"We emphasized the site in 880 in Hayward because of all the sites, it was the one that stood the best chance of benefitting from ejecting the carpool lane," he says. "And even that site – the best candidate – ends up being much worse off."

This could be a case of best intentions yielding worse results. The data shows that since California ejected those 85,000 hybrids, traffic in all lanes is moving as much as 10 miles per hour slower. In the regular lanes that's understandable – there are more hybrids, more competition. But surprisingly, the drivers in the carpool lanes are moving slower, too, because those drivers are going so much faster, they feel a need to slow down.

"The point is, nobody's better off. Even if carpool drivers aren't much worse off, they're still worse somehow," says Cassidy. "So if you would get some of those hybrids back into the carpool lane, and indeed add a little bit more of the regular lane traffic into the carpool lane, everybody would be better off, including those in the carpool lane. It's kind of counter-intuitive, but the data on this are very clear."

As a remedy, Cassidy suggests the state allow hybrids to go back into those lanes and let them mix with the electric cars, the hydrogen cars and the natural gas vehicles. He notes that in January a pending federal program will also allow some 40,000 plug-in hybrids into those lanes, Some may say that will clog them up again, but Cassidy says it will take many more cars than that.

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