Drivers traveled about 185 billion miles on state highways from December 2013 through November 2014, up almost 5 billion miles, or 2.6 percent, from the prior year, according to estimates from the California Department of Transportation. That's the largest traffic jump since 2003.
Typically, California's traffic flow is considered an indicator of economic well-being -- with bad traffic often accompanying a strong economy. Before the recession, commute-hour jams correlated with a prolonged boom in hiring and housing construction. More jobs mean more people driving to work, more people buying cars and more people willing to spend on travel.
Conversely, the free-flowing commutes of the recession were the natural outgrowth of furloughs, layoffs and a stalled economy that meant fewer construction and delivery trucks on the road.
"Congestion is going to be right back where it was and probably worse," said Tom Turrentine, a research anthropologist at the UC Davis Institute of Transportation Studies.
Highway traffic in the state grew by an average of 3 percent annually between 1973 and 2003. That growth continued in the pre-recession years, albeit much more slowly: The number of miles traveled on state highways grew by 1.4 percent between 2004 and 2007.
Between 2007 and 2011 -- as the economy tanked -- highway traffic fell by 3 percent.
At the height of the recession, about 12.5 percent of Californians who wanted work couldn't find it. Today, the state's unemployment rate stands at 7 percent. The difference between those two figures represents almost a million workers, most of whom commute every weekday.
The recent dive in gas prices has amplified the trend, analysts said: Frugal drivers travel more when gas is cheap.
"Probably the biggest reason (for the increase in traffic) is the pretty sharp drop in the price of gasoline," said Kent Hymel, a professor of economics at California State University, Northridge, who has published studies on the state's traffic patterns. "It was over $4 a gallon; now, it is down to about $2.60."
The twin engines of an improving economy and cheaper gas have sparked a small boom in car sales, Hymel and others said. Californians drive more when they aren't trying to squeeze another few months out of their jalopy.
While the spike in traffic signals a healthier economy, experts are quick to note the downside: More cars on the road translates to more agonizing commutes. And the extra exhaust hurts the state's efforts to curb greenhouse gas emissions.
While many California cities are working to increase transit options, the roughly 900,000 people who commute to work via public transit are vastly outnumbered by those who drive. Almost three-quarters of the state's workers -- 12.2 million -- commute alone in their cars. Californians spend, on average, about 28 minutes each morning on their commute, roughly 10 percent higher than the national average.
Vehicle traffic is "a major contributor" to greenhouse gases, accounting for about 30 percent of the state's emissions, said Kanok Boriboonsomsin, an associate research engineer at the Center for Environmental Research and Technology at the University of California, Riverside.
The decline in vehicle traffic during the recession was a chief reason California was able to make significant gains toward reducing emissions, he added. The state has committed to cutting greenhouse gas emissions to 1990 levels by 2020, and is on track to meet that goal.
The growing popularity of cars that burn less gas and emit less pollution will soften the environmental impacts, Turrentine said. But he noted those gains will disappear if Californians decide to buy larger cars in response to lower gas prices.
Traffic figures for the Sacramento region aren't available yet for 2014. Gordon Garry, director of research and analysis at the Sacramento Area Council of Governments, predicted the region has not experienced as much traffic growth as the rest of the state, because the economy hasn't bounced back as fast.
Still, a small amount of traffic growth can cause a lot of congestion, because area freeways are already packed, Garry said.
In 2007, the last time statewide traffic counts were this high, Sacramento drivers spent, on average, about 50 hours a year stuck in slow freeway traffic, SACOG figures show. During the recession, that average fell by more than 25 percent -- five times more than the decline in vehicle traffic. That means congestion also could grow exponentially as traffic increases.
"When you are near capacity, just a few more vehicles has a ripple effect on the road you are on," Garry said.
Call The Bee's Phillip Reese, (916) 321-1137.
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