But engineers at NASA, Boeing Co. and elsewhere say the basis for a flying car is there. People have been building, or trying to build, such vehicles for decades.

The problem is, those ideas have generally required both a lot of money and the skills of a trained pilot. And melding cars and planes hasn't always been very successful.

"When you try to combine them you get the worst of both worlds: a very heavy, slow, expensive vehicle that's hard to use," said Mark Moore, who heads the personal air vehicle division of the vehicle systems program at NASA's Langley Research Center in Hampton, Va.

The goal isn't just to create a neat gizmo: These vehicles will become more appealing — and necessary — as highways and airport hubs grow more clogged, and commutes more distant.

At NASA, the first goal is to transform small airplane travel. Right now, really small airplanes are generally costly, uncomfortable and loud and require months of training and lots of money to operate; that makes flying to work impractical for most people.

Within five years, NASA researchers hope to develop technology for a small airplane that can fly out of regional airports, costs less than $100,000, is as quiet as a motorcycle and as simple to operate as a car. Although it wouldn't have any road-driving capabilities, it would give regular people the ability to fly short distances.

To make flying simpler, NASA is working on technologies that would automate more pilot's functions.

In 10 years, NASA hopes to have created technology for going door-to-door. These still wouldn't be full-fledged flying cars — instead, they'd be small planes that can drive very short distances on side streets, after landing at a nearby airport.

In 15 years, they hope to have the technology for larger vehicles, seating as many as four passengers, and the ability to make vertical takeoffs.

It will probably take years after these technologies are developed before such vehicles are actually on the market. And Moore says it will take about 25 years to get to anything "remotely 'Jetsons'-like," a reference to the futuristic cartoon that fed many flying car fantasies.

Researchers at Boeing in Seattle are already thinking that far ahead: They've created a miniature model of a sporty red helicopter-car hybrid that is helping the aerospace giant understand what it would take to make flying cars a reality.

Lynne Wenberg, senior manager on the project, said the goal is to make a flying car that costs the same as a luxury vehicle, is quiet and fuel-efficient and easy to fly and maintain.

Boeing is especially interested in the broader problem of figuring out how to police the airways — and prevent total pandemonium — if thousands of flying cars enter the skies. No one wants to be cut off, tailgated or buzzed a little too closely by a student driver at 1,000 feet.

"The neat, gee-whiz part (is) thinking about what would the vehicle itself look like, but we're trying to think through all the ramifications of what would it take to deploy a fleet of these," said Dick Paul, a vice president with Phantom Works, Boeing's research arm.

Smaller companies are working on flying car technology as well. Davis, Calif.-based Moller International has already built a prototype of its Skycar. The streamlined vehicle — think sports car meets the hovercraft Luke Skywalker drove in "Star Wars" — is designed to make vertical takeoffs, fly around 700 miles and drive short distances.

Jack Allison, who retired as a vice president at Moller but still works there regularly, said Skycars are expected to start at around $1 million and require pilot's training. It's not yet clear when they'll be available, but Allison says demand is already there: More than 100 people have put down a $5,000 deposit.

While researchers are already working on some level of automation to make flying small planes easier, the ultimate goal would be to have a vehicle that is considerably smarter than what's available today.

Ken Goodrich, a senior research engineer at NASA, said one concept under discussion is technology that runs in "h" mode, which stands for "horse." The idea is that a horse, unlike a car, is more likely to try to avoid other objects and may even know how to find its way home.

But Goodrich said he's not sure that the fantasy of the flying car ever would or should become a reality. He questioned whether having flying/driving vehicles throughout the country might end up being too noisy, disruptive and impractical.