Study: Ending Hybrids’ Carpool-Lane Access Slowed Traffic For All

LOS ANGELES (CBS) — The end of a California program, that granted access to carpool lanes by solo drivers of qualifying hybrid cars, has slowed traffic for everyone, according to research at the University of California, Berkeley.

Hybrid cars, with the yellow “Access OK” stickers, first appeared in California’s carpool lanes in 2005 as part of an incentive for drivers to buy low emission vehicles. That program ended on July 1, affecting some 85,000 vehicles.

One might assume that after the program’s end, traffic in the carpool lanes would lighten, while traffic in other lanes would become more congested, but transportation engineers at UC Berkeley’s Institute of Transportation Studies (ITS) found otherwise.

“Our results show that everybody is worse off with the program’s ending,” said Michael Cassidy, UC Berkeley professor of civil and environmental engineering. “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.”

The study found that moving hybrids out of carpool lanes slowed the general flow of traffic, as one might expect. However, the speed of the carpool lanes are influenced by the speed of adjacent lanes, the researchers said.

When the hybrids were moved out of the carpool lanes, they slowed the general traffic flow, which then slowed the flow of the carpool lanes, according to the study.

“As vehicles move out of the carpool lane and into a regular lane, they have to slow down to match the speed of the congested lane,” explained Kitae Jang, a doctoral student in civil and environmental engineering. “Likewise, as cars from a slow-moving regular lane try to slip into a carpool lane, they can take time to pick up speed, which also slows down the carpool lane vehicles.”

A new proposed program for 2012, that would allow 40,000 super-clean plug-in-hybrids or hydrogen-powered internal combustion engine vehicles to use carpool lanes, is awaiting federal approval.

But researchers at UC Berkeley do not believe it will be enough to relieve the congestion.


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