By 5:30 a.m, there are already enough cars filling southbound Highway 101 toward Petaluma to make Gus Kouninos grateful for the new third lane running over the Cotati Grade.
But on his evening drive home, the Santa Rosa resident can only look at the new construction in frustration. The third lanes between Cotati and Petaluma are closed to solo drivers from 7 to 9 a.m. and 3 to 6:30 p.m. during the commute crunch.
"You've only got motorcycles and a select few who are able to use it," said Kouninos, who works for a beverage company in Petaluma. "When you're in traffic and you see that lane empty, you're like, 'Man that's a third of the traffic that could be over there.' "
The exasperation is shared by many Sonoma County drivers who've endured traffic delays and detours during years of widening of Highway 101 only for the results to be off limits to them when the lanes are needed most.
But advocates of car-pool lanes maintain they're a wise investment, especially for the time when growth and a revived economy add more vehicles to the road.
"People are quite right to ask is this the most efficient use of the lane," said Elizabeth Deakin, a professor of city and regional planning at UC Berkeley. "They also ought to ask the question if it will be in five years."
To date, however, Sonoma County workers haven't exactly demonstrated a strong interest in the diamond lane.
Census figures showed 10 percent of them shared rides to work in 2010, down from 13 percent in 2000 and 1990.
In 1980, the first time the Census Bureau started tracking the number, 16 percent of local workers shared rides.
The decline mirrors a nationwide trend. According to census data, the percentage of Americans who commuted in a shared vehicle dropped in half between 1980 and 2010 despite the addition of billions of dollars of infrastructure to encourage them.
The slide is rooted in a multitude of factors, including the increased affordability of dependable used cars, said Alan Pisarski, a consultant who studies transportation.
At the same time, Americans' work habits have changed with fewer workers sharing schedules, Pisarski said.
"It's harder and harder to find someone who's going where you're going and going when you're going," he said.
Many of those who do share rides are family members who would do so regardless of enticements, he said.
But despite the downward trend, the investment in local car-pool lanes is continuing.
Later this year, Caltrans expects to open a third lane over the Wilfred Avenue interchange, closing the gap in what will be a continuous car-pool lane running from Windsor to Petaluma.
Crews also will begin work on projects south of Petaluma that will set the stage for future car-pool lanes to Novato, the last stages of the estimated $1 billion widening of the Highway 101 corridor between Sonoma and Marin counties.
Caltrans spokesman Robert Haus said the problem with car-pool lanes tends to be there are too few of them forming a fragmented network, not that there are too many.
Until 2009, carpoolers going through Marin County to San Francisco hit a gap in the HOV (high-occupancy vehicle) lane in San Rafael, the most populous part of Marin County, a major disincentive to organize rides, he said.
But as car-pool lanes grow to the point that a lane extends from Windsor to the Golden Gate Bridge, he's confident it's going be an increasingly attractive option.
"That is going to make a good difference," he said.
Perhaps the most persuasive argument for pursuing car-pool lanes, however, may be one of sheer practicality.
There is no government mandate to build car-pool lanes, but the federal Clean Air Act makes it extremely difficult to add lanes to freeways in many areas without making them HOV, said Robert Poole, director of transportation policy for the Reason Foundation, a libertarian think tank.
Even those who may never deign to share a car with someone may benefit. HOV lanes tend to reduce lane changing - the real devil of traffic jams - as carpoolers stay in their lanes and single drivers have fewer options to change, said Michael Cassidy, a transportation engineering professor at UC Berkeley.
The calming effect can result in up to a 20 percent improvement in flow in neighboring lanes, said Cassidy who co-authored a 2009 paper on the topic.
"Even when a car-pool lane is about half-filled, the advantage that is brings thanks to reduced lane changing makes regular drivers better off than if the car-pool lane was turned over to regular traffic," he said. "So many regular drivers are cursing the carpoolers, but they are mistaken. Their lives are better off because of them."
Still, Sonoma County car-pool lanes appear to be running well below 50 percent of capacity, the threshold Cassidy uses for establishing when a HOV lane's use becomes beneficial to drivers in other lanes.
A 2010 Caltrans study found that on a typical day nearly 4,000 vehicles used the northbound lanes of Highway 101 from Highway 12 to River Road during the peak time of 5 to 6 p.m.
About 450 of them were in the car-pool lane, accounting for less than a quarter of the lane's vehicular capacity. Transportation officials consider a highway lane to be capable of carrying up to 2,000 vehicles an hour.
Some hope that new technology can give such numbers a jump. The Climate Protection Campaign, a Santa Rosa-based nonprofit, is working on an Internet app to allow people to exchange ride-sharing information on their smartphones and other devices.
The group has been working with students and staff members at Santa Rosa Junior College, which issued just five car-pool permits this year, despite offering extra parking for those sharing rides.
"Imagine if we could take 1 percent of cars off the road, that would have a huge impact not only on congestion but on greenhouse gas emissions," said Ann Hancock, Climate Protection Campaign's executive director.
News Researcher Teresa Meikle contributed to this story. You can reach Staff Writer Sam Scott at 521-5431 or sam.scott@pressdemocrat.com.
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