Onboard computers relay the sharp drop in speed to sensors in the pavement or alongside the freeway. Computers on a Ford Mustang trailing 50 yards behind receive the news and automatically slow the car. The driver does little more than steer.

Thanks to the automatic braking system, there's no rear-end crash. No massive backup. The Beemer and Mustang move on.

High-tech gizmos may be the best hope of relieving congestion on California's aging interstate highways. But at this point, the system is more like a '60s-vintage jalopy than a space car from "The Jetsons." Fifty years after the interstate system was born, conditions of existing roads are so poor that it's doubtful California can afford to build for the future and keep its roads free of potholes at the same time.

California has the most congested urban interstates in the nation and ranks high among states with the most crumbling federal roads. Each year, the average South Bay driver pays $689 in pothole-related car repairs, according to Transportation California, a highway advocacy group.

The state has neglected its highways for two decades and faces a transportation shortfall of more than $100 billion. In 2004, California spent $137 per capita on transportation, compared with $218 nationwide. And consider this sobering fact as you fill up for $3 a gallon: The state's 18-cent-a-gallon gas tax would have to be at least doubled to meet today's needs.

How did it happen? Partly politics, partly growth: The wild and carefree Land of the Little Deuce Coupe of decades ago has been transformed into Gridlock Central thanks to Gov. Jerry Brown's no-new-highway mantra, Howard Jarvis' anti-tax movement and millions more drivers.

Still, the dreamers dream on. Future plans may rely less on pavement and more on technology, trying to squeeze more cars into the same number of lanes. Within a few years, major tests will be conducted on Interstate 580 and I-680, and possibly I-880, to see how well toll lanes, metering lights and collision avoidance sensors can help cars move speedily and safely.

"Cars are getting smarter and smarter," said Randy Iwasaki, Caltrans' chief deputy director. "Think back to what a cell phone could do 10 years ago and what you can do now. That technology is coming to our cars."

Growing pressure

-- State population keeps growing

With the state Department of Finance predicting that California's population will grow from 37 million to nearly 50 million by 2025, interstates will be hard-pressed to handle everyday traffic -- from big rigs pouring out of ports in Long Beach, Los Angeles and Oakland to commuters slogging down the Nasty Nimitz. Traffic planners predict congestion in the Bay Area will grow 77 percent by 2025, unless changes are made.

"We are very alarmed at the state of our road system," said Sunne Wright McPeak, California's secretary of business, transportation and housing. The interstate system, she said, is "at a crossroads."

A California Transportation Commission report is more blunt: The system is in "a shambles."

It's not only experts who recognize the problem. Ordinary drivers do, too, when they cross the state's borders.

Sarah Robeson of Mountain View was stunned when she drove to the Midwest this summer.

"By far, the worst of the states' interstate road conditions was California," said Robeson, 27, a clinical research associate at Stanford. She recalled the construction-induced nightmare of a Friday evening rush hour on I-80 near Omaha, Neb. But that, she said, "was an absolute pleasure compared to driving anywhere in California."

Will Booth, a San Jose marketing consultant fresh from a three-month, 12,240-mile trip through 19 states and five Canadian provinces, agreed that California's roads were the worst of the worst. "Interstate 80 from Truckee to Blue Canyon and I-680 are horrible," he said.

State of disrepair

-- Billions needed just to stay put

Fixing California's interstates, some virtually untouched since President Dwight D. Eisenhower gave a green light to build the system in 1956, will be costly. The California Transportation Commission estimates that $105 billion is needed over the next decade just to keep commutes no worse than today, when a 33-mile drive on I-880 from Oakland to San Jose can take an hour or longer. Other agencies say the shortfall could be as high as $160 billon.

Traffic crawls on three of four miles of interstate roads that run through California's major cities. The pavement on 38 percent of the state's interstates -- nearly two of every five miles -- is in poor or mediocre condition, compared with the national average of 17 percent. Only the District of Columbia, Rhode Island, New Jersey, Alaska and Hawaii have worse roads.

Voters will be asked to approve a $19.9 billion transportation bond this fall, with $4.5 billion set aside for improvements along main freeway corridors. But only $250 million would be directed to technology advances.

General Motors showcased automatic braking technology at a conference in San Francisco last year. And by the end of the decade most new cars will provide traffic information on dashboard screens, with blinking hot spots to catch a driver's eye and colored lines suggesting alternate routes.

Eventually, cars within 300 yards will send and receive warnings about sudden changes of speed. But manufacturers have yet to agree on a standard format to exchange the information.

"GM cars could talk with each other, but no other manufacturer's cars," said John Bonds, a Cupertino-based specialist in intelligent highway designs for the PBS&J engineering and consulting firm. A sophisticated communication system could take at least 10 years to develop. Until then, Bonds said, "we'll be stymied from employing smart cars that keep dumb drivers from doing unsafe things."

Much sooner, perhaps in three to five years, motorists will find toll lanes on I-580 from Pleasanton to Livermore and I-680 from Sunol to Milpitas that will let solo drivers pay their way into the carpool lane for as little as 25 cents in off-peak hours or several dollars at congested times.

Toll lanes are already in use on Highway 91 in Orange County and on I-15 in San Diego. The Valley Transportation Authority will study tolls on Highways 85 and 101.

"This is not pie-in-the-sky," said Bob Poole, head of the Reason Foundation, a libertarian think tank that is pushing to open up all carpool lanes to solo drivers willing to pay for the privilege.

Worthless data

-- Drivers complain about hotline

When David Atala drove down I-880 in July, he ran into horrendous traffic. A growing sinkhole had formed at The Alameda, forcing the state to shut down one lane for the afternoon. A frustrated Atala called the state road hotline -- (800) 427-7623 -- and heard a message that riled him even more: "There are no adverse conditions."

"To me, that number is worthless," he said.

Caltrans' Iwasaki knows the challenge. As the state forges ahead with high-tech approaches, "it has to be credible. If it's not credible, people will stop using it."

Indeed, it's hard to bank on a system so lacking. To give drivers alternatives on crowded Bay Area freeways, Caltrans needs:

-- Lane detectors every half a mile. But only 1,200 of 3,200 detectors have been installed.

-- Another 700 closed circuit TVs to monitor traffic. Only 300 are in use.

-- About 200 large electronic message boards. Only 96 are installed.

-- More than 1,100 ramp meters; only 210 ramps now have them.

Regional officials have committed $160 million to technology, such as electronic signs, FasTrak and the 511 road hotline for the Bay Area. And they pledge an additional $500 million, spread over 20 years.

Despite the investment, glitches make motorists leery of trusting traffic reports on radio and messages on electronic freeway signs.

Just one example: Traffic came to a halt on Highway 101 this summer when a message board in Mountain View warned of upcoming work at I-380 and Highway 82.

Oops. The sign should have read I-880, but some light bulbs were burned out.

The state has doubled funding for repaving from $326 million in fiscal year 2005 to $666 million this year. But that's far below the $942 million spent in 2001. By 2019, Caltrans intends to repave 13,592 of 18,453 miles of lanes throughout the state.

Big projects are also under way -- rebuilding the Mission-880 and Coleman-880 interchanges, adding carpool lanes on I-580 and widening I-205.

Norm Mineta, who recently resigned as U.S. secretary of transportation, had asked President Bush to hike the federal gas tax by 6 cents over several years for road relief. But Bush said no to the proposal, as well as one to link the gas tax to inflation.

Mineta says a "cultural change" is needed in Americans' attitudes toward the way roads are funded.

"Their reaction is that 'I'm already paying a gas tax, so why am I paying a toll on top of that?' " Mineta said. "A toll enables you to get from Point A to Point B faster, but is that only going to be for the Lexus drivers? I don't think as a public policy that we really have thought that out yet. But it has to be addressed."

Traffic delays cost California $25 billion a year in lost wages and productivity. That's one reason the state is again shifting the sales tax on gas purchases from the general fund to target transportation issues. That will add $1.3 billion a year for road and rail upgrades.

Then there's the November bond measure. But most experts say it won't be a cure-all.

"One can only view the $20 billion for transportation in the bonds as, at best, a very modest down payment on what is really required," said Poole of the Reason Foundation. "Given that today's freeways and interstates are grossly overloaded much of the time, to think that we could possibly get by without major capacity additions is ludicrous and irresponsible."

No easy fix

-- Cynical drivers see no change

Many commuters are skeptical that road woes can be solved by technology without extra lanes or more mass transit.

"I would like to believe the smart highway-car thing would work, but I'm not very optimistic," said Lisa Gaunt, a writer at Hewlett-Packard.

Neither is Bob Davenport, 60, of Fremont, who recalls traffic jams on Bay Area bridges after FasTrak was put in place. "We can't get reliable, fast, accurate information on radio stations about imminent traffic jams forming due to accidents," he said. "So why should we expect a more complex system to be implemented and to work any better?"

But traffic gurus insist that one day onboard computers will maneuver cars and control spacing, speed and braking distances. Computers will warn of accidents and congestion -- and give drivers immediate updates on their commutes, experts say.

"I don't think of it as a dream. We are looking at it as a real opportunity to handle future traffic. Some people say it is unrealistic, but the potential is there to keep traffic moving."

That from Caltrans director Leo Trombatore.