Carpool Hybrids Booted, Traffic Gets Worse

Back in 2005 California legislators had a great idea. As in incentive to wean people off the internal combustion engine they allowed single-driver hybrids to join hydrogen fuel cell, fully electric and compressed natural gas cars into the carpool lane. Like most good ideas, this one has come to an end, with the expected crummy results.

Some 85,000 low-emission vehicles have gotten the coveted yellow stickers that gave them entry into the carpool lanes, but critics of the perk argued that solo drivers of hybrid cars were clogging up the lanes for carpoolers. Now, according to transportation engineers at the University of California, Berkeley, booting hybrids from the carpool lanes has actually slowed traffic.  Researchers used traffic flow theories and six months of data from roadway sensors measuring speed and congestion along all freeway carpool lanes in the San Francisco Bay Area. They used the information to predict the impact on vehicle speed of the hybrids’ removal from carpool lanes. Additional data collected after the program’s July 1 expiration supported their predictions.

prius-1 via toyota

Image via Toyota

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

A carpool lane along a four-mile stretch of I-880 in Hayward, according to the report, saw a 15 percent reduction in speed after single-occupant hybrids were expelled. The report explains that traffic speed in the carpool lane is also influenced by the speed of the adjacent lanes. Moving the hybrids into the neighboring lanes increases congestion in those lanes, which in turn slows down the carpoolers. “Drivers probably feel nervous going 70 miles per hour next to lanes where traffic is stopped or crawling along at 10 or 20 miles per hour,” said Cassidy. “Carpoolers may slow down for fear that a regular-lane car might suddenly enter their lane.”

Steve Duda lives in West Seattle, WA with three dogs and a lot of outdoor gear. A part-time fly fishing fishing guide and full-time writer, Steve’s work has appeared in Rolling Stone, Seattle Weekly, American Angler, Fly Fish Journal, The Drake, Democracy Now! and many others.