What will cars and trucks look like 20 years from now? What kind of architecture will they have? What design themes will there be after "cab forward" and "new edge" have run their course?

Not surprisingly, automakers don't want to say. It would mean giving a highly proprietary peek into the most advanced of advanced planning. Plus, who can be sure where they'll be headed that far in the future?

Instead, automakers point to their annual parade of concept cars and invite inquiring minds to draw their own conclusions. Unfortunately most current concepts don't offer too many clues as to what automakers might be up to in 2020. Concept cars were once whimsical flights of fancy designed purely for entertainment of the car-buying public, but now more often than not, they are deadly serious affairs created to gauge public reaction to new designs only a few years from production.

Even so, given the auto industry's long product-development lead times and even longer product cycles, a few educated guesses can be made: basically sound concepts such as Heritage Design likely will still be going strong in 2020. It also looks like new body structures, including space frames and space frame unibody hybrids, may be a strong trend in the next 10 to 20 years. And of course, designers continually will strive to provide more usable interior space while they rein in unwieldy exterior proportions.

In terms of basic styling, the bold lines and crisp edges defined by "new edge" and cars like Cadillac's Evoq could still have legs by 2020. "Heritage" design themes that try to strengthen brand equity by borrowing design cues from the past likely will be in full bloom 20 years from now.

BMWs still will sport their distinctive twin-kidneys and Mercedes-Benzes likely will have a trademark grille; Lincoln will have established a distinctive new look, and Cadillac's edgy "Art & Science" theme will be old hat.

Carl L. Olsen, chair of the Transportation Design Dept. at the Center for Creative Studies (CCS) in Detroit, suggests that automakers also are developing deliberate "nationalistic styles" that will create specific aesthetics and design themes that will connote a French car, a German car - or an American car - that will give them an easily distinguished identity in diverse world markets.

CCS, for instance, now is working on an "Americana" project with DaimlerChrysler Corp. that asks students to explore the history of American car design and create a new aesthetic.

Other new design themes can be seen emerging - particularly in Europe - where a new class of small cars that emphasize aerodynamics, utility, crash safety and ultra-high fuel economy are being developed. These include the Mercedes A-Class, Audi A2 and others.

General Motors Corp.'s Adam Opel G90 concept aims to put those two to shame. It's built around an aluminum space frame and is powered by an existing 60-hp, 3-cyl. direct-injection gasoline engine and is capable of 64 mpg (3.7L/100km) while still delivering decent performance. The tail section has a striking teardrop shape that reduces air turbulence and drag. Opel wants to show it's possible to make a reasonably priced car with exceptional economy without having to resort to exotic engineering solutions.

When the Chrysler side of DaimlerChrysler AG is asked what comes after cab-forward design, it points to the Java, which debuted at the Frankfurt Motor Show. Tom Gale, executive vice president of Chrysler Product Development, Design and Passenger Car Operations, says it represents a fresh approach to an important European segment.

Its "one-box" profile and "passenger priority design" provides remarkable interior space and utility for a relatively small vehicle. It's about as big inside as Chrysler's upcoming PT Cruiser, yet it is 20 ins. (50 cm) shorter than the PT on the outside. Java emphasizes a tall architecture and panoramic seating for drivers and passengers for a sport/utility-like "in-control" feeling.

If you want a truly futuristic concept, though, you have to go back a year or two to the 3-wheel Mercedes F 300 Life-Jet, which is part car, part motorcycle. Pictured on our cover this month, it shows that even if environmentalists outlaw SUVs and sports cars in the next century - and gasoline shoots up to $10 per gallon - we still might be able to have fun driving.

Looking like a 1950s "future car," it's styled like a jet and promises the cornering dynamics of a motorcycle and the safety and comfort of a car. Using the engine, transmission and other components from the A-Class parts bin, the Life-Jet has an extruded aluminum space frame with cast nodes that form a very strong structure that weighs only 196 lbs. (89 kg) but is claimed to be able to absorb high crash forces. On the underside, the chassis is faced with double-skinned panels that sandwich a new aluminum foam material for additional strength and sound insulation. Total curb weight is just 1,760 lbs. (800 kg).

It's easy to imagine seeing Life-Jets in 2020. Yet remember that in 2020 there still will be millions of today's cars still on the road. A recent report by the Motor & Equipment Manufacturers Assn. says that the number of 15-years-old-and-older vehicles on U.S. roads is expected to be 18.5% and reach 40 million units within the next 4 years. Between 1990 and 2002, the number of older vehicles is expected to nearly double, from 20.6 million to 39.7 million.

With today's higher quality vehicles and corrosion-resisting materials, the prospect of millions of giant old-style Ford Excursions, Chevy Suburbans and Dodge Ram pickups lurking on the highway in 2020 looms large. Even if fuel prices shoot up and environmental pressures become oppressive, how many consumers - especially Americans - will eagerly trade in their truck keys for small fuel sippers when they know they still will be sharing the road with those monsters?

Looking out 20 years is a dicey business at best because so much can obviously change. Then again, using history as a guide, perhaps there will not be nearly as much change as we might expect.

For instance, many might consider it ludicrous to try to guess what vehicles might look like 50 years from now. Yet Mr. Olsen at CCS points out that the '49 Ford remains the archetype of the modern passenger car. It was the first vehicle design that eliminated the pronounced bulges that separated the wheels and fenders from the rest of a car's lines. Its basic size, weight and powertrain aren't dramatically different from today's family car.

You could argue that vehicle architecture is drastically different from what it was 20 years ago. The late 1970s and early '80s saw a massive shift in the U.S. away from big body-on-frame, rear-drive cars to smaller, more space-efficient unibody front-drive platforms. Yet the enormous popularity of pickup trucks and SUVs - most of which still feature old-fashioned rear-drive, body-on-frame construction - continues to stall the trend.

But after a dull period of about 10 years, automakers do seem to be getting impatient with standard body-on-frame or unibody construction for new products. Honda Motor Co. Ltd. recently introduced its S2000 roadster which features an unconventional "high X-bone frame" design that uses a strong, highly rigid, boxed-section central floor tunnel to connect - like the body of a spider to its legs - to the side members on the same horizontal plane. Honda engineers say this technique provides an open-body car with the rigidity of one with a fixed-roof.

Fiat SpA, the world's sixth largest automaker, is becoming a huge proponent of using structural space frames for vehicle bodies rather than conventional technology.

Fiat's chief executive, Paolo Cantarella, says that in 10 years every car made by Fiat Auto - including Alfas, Lancias and Fiats - will be built around the extruded steel space-frame principle, which is pioneered by its current Multipla model.

Fiat apparently is convinced that space-frame technology, and the production and design flexibility it offers, brings huge advantages to a common platform policy. "We can change the wheelbase and tracks easily, Mr. Cantarella says. "You can use engine subframes, or not, and incorporate different engines and gearboxes, different suspension systems - basically anything."

But U.S. automakers already have been down the space-frame road, with little success. The concept of making a "birdcage" vehicle structure and then just hanging on panels made of steel, plastic or aluminum has been around since at least the 1950s. And it always has been alleged that such a structure allows many platform derivatives and the ability to restyle vehicles at very low cost.

Yet so far automakers have had great trouble manufacturing successful high-volume space-frame vehicles. GM tried twice in the 1980s with the plastic-paneled Pontiac Fiero and its now infamous "dustbuster" APV minivans, and both were failures. Don't expect to see GM gushing about the possibilities of space frames anytime soon. It already has been there and done that. o - with Peter Robinson