Northern California's first test of charging higher bridge tolls during rush hour resulted in speeding up Bay Bridge travel, UC Berkeley researchers conclude in a study.

After Bay Bridge weekday tolls were changed in July 2010 to $6 during rush hours and $4 at other times, travel time dropped for motorists from all three East Bay approaches, said researchers hired by the Bay Area Toll Authority.

The biggest improvement was a 16-minute saving for drivers headed north on Interstate 880 from Union Street in Oakland to the toll plaza between 7 and 8 a.m. The savings were a more modest 11 minutes from westbound Interstate 580 and nine minutes for southbound Interstate 80.

"Travel to the bridge speeded up," said John Goodwin, a spokesman for the toll authority, a regional agency that sets the tolls. "It's moving faster because we're distributing the peak load of traffic over a longer span of time. That's what congestion pricing is about."

The overall travel time reduction was about 4 percent during 6 to 8 a.m., researchers said.

Some drivers shifted their travel to outside the rush hour, while others switched to public transit, the research team concluded.

The study is to be presented to the toll authority oversight committee at a meeting 9:30 a.m. Wednesday in Oakland.

In another finding, the researchers said carpool use on the Bay Bridge dropped sharply, by 4,365 vehicles a day -- a 26 percent plunge -- after July when carpools no longer got a free ride across the bay.

The rush hour toll is now $2.50 for carpools of three or more people.

Some 54 percent of the vehicles that stopped carpooling did so because of the new toll, the UC Berkeley researchers concluded after conducting interviews with commuters.

"However," the team wrote, "the carpoolers did not just switch to driving alone." Some switched to BART, which showed a modest bump in ridership on its Transbay Tube service between Oakland and San Francisco, according to the study. AC Transit bus service across the bay remained flat, Goodwin said.

Some drivers stopped using the carpool lane because they were using it illegally without three occupants in a vehicle and feared being caught, Goodwin said.

Toll lane scofflaws used to be caught only when California Highway Patrol officers witnessed the illegal use of the free lane. But since last year when electronic tolls have been collected in the carpool lanes with the FasTrak system, violators are photographed and sent penalty notices.

The toll authority sets different tolls for the Bay Bridge because it's busier than others in the region.

In July 2010, the toll authority raised the toll from $4 to $5 on the Richmond-San Rafael, Benicia-Martinez, Carquinez, San Mateo, Antioch and Dumbarton bridges.

The authority said it needed more money for seismic retrofits on the state-owned bridges and to offset reduced bridge traffic and toll revenue over several years and higher financing costs because of tight credit nationwide.

Contact Denis Cuff at 925-943-8267.

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