Orange County has pursued a different approach, adding 646 miles of freeway lanes -- about half of which are on privately funded toll roads -- at a cost of more than $5.7 billion. In one of the county's largest projects, the 5 Freeway was expanded from six to 14 lanes in many places.
Meanwhile, Los Angeles has struggled to entice people onto its mass-transit network. In recent months, there appears to have been an increase in rail ridership in response to the surging price of gasoline. But despite the $7-billion investment in light rail and subway lines, transit agencies in L.A. County have not been able to increase their market share. Census data show that as income rises, transit use declines, suggesting that the moment people can abandon buses or rail, they do.
It's not that new construction can't help. Most planners see promise in building lanes to separate big rigs from other traffic and in eliminating railroad crossings at street level.
But there is an ironclad rule that helps account for traffic's mulish persistence: When travel on the freeway becomes easier, more people do it.
"We're not going to clear up congestion with alternatives," Roper said, "because the thing that's going to drive people to alternatives . . . is congestion."
The appeal of the solo drive -- with its promise of freedom and privacy -- remains deep: Between 70% and 80% of commuters in Southern California still go it alone. The latest idea to change that is to make them pay. What if companies charged employees $35 a day for parking? What if cities created car-free zones, as in Europe? What if drivers had to pay for using overcrowded freeways such as the ones that intersect downtown?
High gasoline prices lately have eased traffic on some freeways, experts say, and spurred demand for more fuel-efficient cars.
But Rand Corp. transportation expert Martin Wachs thinks it will take more. Even if fuel hits $5 a gallon, he said, congestion will merely thin at the margins -- meaning shorter rush hours -- rather than evaporate. "I think the price at which people will stop driving is much higher," he said.
In central London, car traffic has dropped 20% since 2003, when the city began charging motorists a fee of about $16 if they wanted to drive into the city center. And there have been other benefits: Bus ridership has surged, and the tolls paid by drivers are being used to improve public transit.
Congestion pricing "has worked around the world in about 100 different places, 100% of the time," Wachs said.
But there is a downside: Levying tolls in crowded areas is the kind of third rail that politicians are loath to approach. The mayor of London endured calls for his ouster after he instituted central city driving fees. In Southern California, motorists tend to scream about even the suggestion of tolls on existing roads.
Brian Taylor, a transportation expert at UCLA and a prominent advocate of tolling, pointed to the success of the tollway between Anaheim and Corona, which opened in 1995.
Motorists pay tolls ranging from $1.20 during off-peak hours to $10 when traffic is heaviest to use Express Lanes on 10 miles of the 91 Freeway. Those who pony up say they save about 27 minutes on their morning commutes and 39 minutes in the evening. Transportation agency polling has found that commuters in Orange County have accepted toll roads, which makes Taylor optimistic that motorists elsewhere also will.
We'll find out soon enough. In April, the Metropolitan Transportation Authority voted to convert some carpool lanes on the 10 and 210 freeways to toll roads. The move came after the federal government said it was prepared to offer $200 million for upgraded buses and rail lines if transportation officials would agree to institute so-called congestion pricing on some freeways.
Donald Shoup, an urban planner at UCLA, has a different idea for making commuting more expensive. He notes that 95% of people who drive to work park free when they get there, and that they would carpool more if there were a financial incentive.
"Everybody expects to park free everywhere they go, and that means that cars are the obvious way to travel," Shoup said. Wachs, of Rand Corp., sees the problem as even more basic. For all the bitter carping, he said, motorists show more tolerance for stop-and-go conditions than for solutions that require personal pain.
"The solutions are not unknown," Wachs said. "The fact that we are inhospitable to all of the solutions must indicate we would rather have the problem as we have it now than solve the problem."