Road Rules on Hybrids May Slow Down Traffic


The California State Legislature passed a regulation banning hybrids and electric vehicles from the carpool lane effective July 1. The wisdom of the lawmakers thought that these special vehicles effectively slow down the carpool lane, increasing inefficiency.

A recent study though has found that denying hybrids rights to drive in the carpool lane only slows down traffic on all lanes of the freeway, including the carpool lane. The study was conducted by Kitae Jang and Michael J. Cassidy of the Institute of Transportation Studies at the University of California at Berkeley.

Through a set of complicated equations and data obtained through roadway sensors, the theory formulated measured speed and congestion rates on freeways along the San Francisco Bay Area six months prior to the July 1 deadline. Then, the same sets of data were obtained in both July and August after effectivity of the ban. The results yielded that all lanes slowed down when the hybrids were not allowed into the carpool lane.

According to the researchers, “Everyone seems to offer.” They further speculated some reasons why the carpool lane slows even further even with the removal of hybrids in the lane. One of them would be those driving in the carpool lane instinctively slows down because going faster than the traffic on the regular lanes feels inherently dangerous.

The researchers added, ““Carpool-lane drivers may be reluctant to travel fast when adjacent traffic is moving at slow, congested speeds. And when regular lanes are congested, lane-changing maneuvers made into and out of a carpool lane may become disruptive and diminish its speeds.”

The carpool lane incentive was introduced as part of a package of benefits for the purchase of low-emission cars. Introduced in 2005, by 2011, over 85,000 low emission vehicles were able to use the lane. Many carpoolers though criticized that many hybrid cars had only solo drivers, thus clogging up the lane for carpoolers.

The results were very different from what the state legislators predicted. This may be due to the presence of additional cars into the freeway thus adding to the congestion. As for the supposed decongested carpool lane, the users of the lane became more cautious because of the lesser number of carpool lane users.

According to Jiang, ““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. 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.”

There needs to be greater studies on the matter in order to fully realize the goals set forth for fuel efficiency in the long run.