Carpool Lanes Don’t Cut Traffic or Pollution, So Let’s Ditch ‘em

Wayne King is director of the Drivers for Highway Safety Transportation Forum, a volunteer organization based in Orange that seeks to promote safe and effective highway systems

Since California’s doomed 1976 “diamond lane” experiment, carpool lanes have come under steady attack by the traveling public, perhaps for good reason. The public long has perceived what is now coming to the attention of academic researchers and objective authorities such as New Jersey Gov. Christine Todd Whitman. When restricted and unrestricted road operations are carefully compared, the unrestricted road that everyone can use provides the most benefit. Any attempt to restrict the natural, free distribution of vehicle traffic makes regional traffic congestion and tailpipe emissions worse.

Why then are California transportation authorities still promoting carpool lanes? A restricted and uncongested carpool-only road should provide a time-savings incentive for travelers to join a carpool. If more travelers choose to carpool, more people will be carried by fewer vehicles, thereby reducing traffic congestion, fuel consumption and tailpipe air pollution. It’s a reasonable assumption, but does the time-savings incentive motivate a significant amount of carpool formation?

In late 1985, a new lane was added to each direction of the Costa Mesa Freeway. The new lanes were opened as a “high occupancy vehicle lane” demonstration project. Without ever testing the alternative mixed-flow lane operation, transportation authorities declared the lanes a “success” within the first few weeks of operation. Now, almost 13 years later, reality does not support the declared success.

By 1990, Caltrans had added carpool lanes to the San Diego Freeway. Both freeways’ carpool lanes were restricted to vehicles with two or more occupants. Had they motivated a significant number of new carpools, the lanes would have become as congested as the surrounding mixed-flow lanes, with a parallel loss of any time-savings incentive. Had that happened, restoring the time-savings incentive would have required increasing the occupancy restriction from two to three or more persons. For whatever reasons, car-pooling has not increased significantly; therefore, carpool-lane vehicle occupancy restrictions have not been increased. The evidence is clear and convincing.


No Orange County traffic reduction can be credited to motivated car-pooling. Notwithstanding the sizable extra installation and operating costs, the lanes have not been effective. Most of the county’s mixed-flow roads remain stop-and-go congested and, ironically, a carpool lane affords a time-savings incentive only when all other roads are congested.

Strangely, the failure of carpool lanes is now documented by the same agencies that continue to promote them. The Southern California Assn. of Governments’ required 1998 Regional Transportation Plan reports that “for a variety of reasons, and despite the near-capacity utilization, the investment in [carpool lane] infrastructure has not resulted in the anticipated benefits for the region as a whole.”

A $3-million 1997 Orange County Transportation Authority study, in dispute with the authority’s public support of carpool lanes, concludes that compared to a similar carpool lane, a mixed-flow lane provides (1) seven times more travel-time savings; (2) 2 1/2 times the freeway decongestion; (3) two times the arterial road decongestion, and (4) 16 times the carbon monoxide reduction. Still another 1997 OCTA study indicates efforts to reduce congestion by restricting road use are counterproductive. But not to be taken in by the evidence, OCTA director and Orange County Supervisor Charles V. Smith recently persuaded the OCTA board of directors to vote down a proposed major review of carpool-lane effectiveness.

Smith should rethink his opposition. The public’s concerns about carpool-lane safety were validated by a 1990 Drivers for Highway Safety Transportation Forum analysis of the California Highway Patrol’s accident records for the Costa Mesa and Riverside freeways. The analysis indicated that the overall accident rate increased after carpool lanes were installed.


Dollar for dollar, mixed-flow lanes allow substantially more vehicles to travel at a constant speed, resulting in shorter travel times and therefore less congestion and air pollution. The evidence is compelling. Gov. Gray Davis should follow Whitman’s lead: (1) Open all carpool lanes for use by all travelers and (2) order the Department of Transportation to abandon all new carpool lane development. For those poised to remind us that carpool lanes are required for federal funding qualification, forget it. According to the OCTA’s director of planning, “There is no specific law or regulation that limits new freeway capacity to being only [carpool] lanes.”