Unintended Consequences: Booting Hybrids from HOV Lanes Slows Traffic

 Hybrid car in the carpool lane, Institute of Transportation Studies, University of California, Berkeley

This past July, the California Clean Air Stickers for HOV Lanes program ended for hybrids. What was the effect of this change? How did it affect traffic flow and congestion? That question was investigated by ITS researchers Prof. Michael Cassidy and Kitae Jang, of the Volvo Center.  Their new ITS report, Dual Influences on Vehicle Speeds in Special-Use Lanes and Policy Implications, analysed traffic data and used models to calculate the impact of the added low-emissions vehicles on the other lanes. Cassidy told the Berkeley Newscenter:

“Our results show that everybody is worse off with the program’s ending,” said Cassidy. “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.”


“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 Jang. “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.”

The paper was also discussed by the New York Times, USA Today, and the LA Times