The state has issued 85,000 decals allowing lone motorists in hybrids to use the lanes, and there has been a clamor for officials to issue more as the fuel-efficient cars gain in popularity. Some carpoolers have complained that the addition of the hybrids has worsened traffic and slowed the carpool lanes. But a recent Caltrans study concluded that there was no clear indication that hybrids had significantly clogged the lanes.
Some transportation agencies and experts have suggested increasing the minimum number of people allowed to use carpool lanes to three occupants from two. Three per car is already the minimum during peak hours on the El Monte Busway on the San Bernardino Freeway and on most roadways leading to the toll plazas on Bay Area bridges. Two per car is the standard in most other parts of the state.
Raising the number would reduce carpool lane traffic -- something Foothill Transit and other bus agencies like.
But it would come at a price.
"If they switched to three-plus, it would create 'empty lane syndrome' for a while," said Robert Copp, chief of the division of traffic operations for Caltrans in Sacramento.
Carpool lanes would be emptier, not working at a great capacity, and some current users would be forced into regular lanes, worsening traffic there.
But the idea also appeals to some traffic experts who have long sought ways to add toll lanes to Southern California freeways.
Robert Poole of the Reason Public Policy Institute suggests that the extra capacity in the carpool lanes could be used by charging lone motorists a toll to use them. Revenue from these tolls could then be used to build freeways.
Under the concept of "congestion pricing," the cost of the toll would rise in such a way as to keep the lanes free flowing.
The Bush administration has made congestion pricing a priority of its transportation policy, earmarking $130 million this year in grants to agencies working on toll road-type projects. Los Angeles County has no congestion pricing program in the works -- and officials believe that's why the region was passed over for federal traffic grants this year.
Toll lanes exist on freeways in Orange and San Diego counties, with the prices changing with the flow of traffic. Fees on the 91 Freeway's toll lanes, for example, approach $10 during rush hour.
Toll lanes on freeways are usually built by private firms -- and efforts to convert existing carpool lanes to allow for tolls would have to clear legal hurdles.
But the carpool lanes have long been controversial. An attempt in the 1970s to convert an existing lane into a carpool lane on the Santa Monica Freeway prompted a revolt.
In response, Caltrans decided it would add carpool lanes only when widening freeways so it would not take away regular lanes.
Some officials do see some bright spots in the traffic woes.
"The good news is that people are using carpool lanes," said Rose Melgoza, a spokeswoman for the Caltrans office in the Inland Empire.