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Booting hybrids from carpool lanes slows everyone down, study says

October 11, 2011|By Ronald D. White, Los Angeles Times

If you're like many California motorists, you probably looked on with envy or perhaps some stronger emotion when those single-occupant hybrids zipped by in the carpool lane. Others who had gone to the trouble of coordinating schedules and establishing real carpool relationships probably weren't too happy with their solitary HOV-lane brethren either.

Surely, fairness was restored over the summer when the interlopers lost their carpool-lane rights; the real carpoolers have seen their speeds increase, right? Wrong.

A UC Berkeley study released Monday says banishing those lone hybrid drivers from carpool lanes has made traffic slower for everyone. As an example, they cited a four-mile stretch of carpool lane on Interstate 880 in Hayward, which has seen a 15% reduction in speed since July 1, when single-occupant hybrids were expelled.

What gives?

Researchers at UC Berkeley's Institute of Transportation Studies said they used traffic-flow theories and six months of data from roadway sensors measuring speed and congestion along all freeway carpool lanes in the San Francisco Bay Area to reach their conclusions.

Among other things, the report's authors found that the additional vehicles in the regular traffic lanes slowed speeds substantially. That slower traffic made it more difficult for carpool drivers to move in and out of the HOV lanes, slowing them down as well, according to the report written by Michael Cassidy, a UC Berkeley professor of civil and environmental engineering, and Kitae Jang, a doctoral student in civil and environmental engineering.

They were examining the end of a program that began in 2005 and concluded July 1 that gave consumers an extra incentive to buy low-emission cars. By 2011, about 85,000 low-emission vehicles were carrying yellow stickers that gave them access to carpool lanes.

"Our results show that everybody is worse off with the program's ending," Cassidy said. "Drivers of low-emission vehicles are worse off, drivers in the regular lanes are worse off and drivers in the carpool lanes are worse off. Nobody wins."

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