courtesy Creative Commons

Transportation engineers at the University of California, Berkeley said the program, which ended July 1, gave consumers an incentive to buy low-emission cars. When they bought a low-emission car, they would be given a yellow sticker that gave them entry into the carpool lanes.

Proponents claimed that these solo drivers were clogging up the lane for carpoolers and the practice ended.

Researchers at UC Berkeley’s Institute of Transportation Studies used traffic flow theories and six months of data from roadway sensors that measured speed and congestion in the San Francisco Bay Area.

Michael Cassidy, a UC Berkeley professor of civil and environmental engineering, and Kitae Jang, a doctoral student, released a report detailing their findings.

“The strength of the study is that we collected data for six months and used theories to make predictions about when hybrids were pulled from carpool lanes,” Cassidy said. “Later, the data showed our predictions were right.”

Cassidy said that no further research is needed because the results were very clear and taken over a long period of time.

The report shows that people are worse off since the program ended. Hybrid cars moving to other lanes caused the traffic in that lane to go slower. Data also showed that cars in the carpool lane moved slower.

“The hybrid vehicles from the carpool lane decreased their speed in the regular lane which then negatively effects the carpool lane,” Jang said.

Some were surprised about the finding that the cars in the carpool lane moved slower after the hybrid cards moved into the regular lane.

“The carpool lane slowed for two reasons,” Jang said. “One reason is high demand. The second reason is that the lane next to it is slow, so people don’t feel safe driving too fast next to the slow, regular lane.”

Overall, the findings of the study were clear: having hybrids leave the carpool lane did not help traffic, but ended up worsening it for all lanes.

“If we take hybrids out of the carpool lane, we worsen the traffic in the regular lane, and the other one slows down,” Jang said. “Discontinuing the hybrid policy reduces speed in the regular lane and then the carpool one.”

In order to increase the speed of both lanes, Cassidy said 2-3 percent more cars need to be added to the carpool lane.

Read more about the study here.

Reach Associate News Editor Hannah Madans here.