Light, ethereal, and nimble, the 2006 Subaru R2 Type S is the face of automotive technology that wears the halo. Drive me, it whispers, and you'll get incredible fuel efficiency. You'll accelerate smartly while burning less imported fuel.

Over there, wearing the horns, is the huge and brutal Bugatti Veyron 16.4, which goes from 0 to 100 kilometers per hour (62 miles per hour) in 2.5 seconds and burns as much as 26.1 liters of gasoline to go 100 km. Drive me, it growls, and you can humble every other vehicle on the road. All you need is US $1.2 million.

Two road machines, for the soul and for the body, for Dr. Jekyll and for Mr. Hyde. Every other car today falls somewhere in between, a tradeoff between gas-guzzling darkness and environmental light. The dichotomy, sharp for a long time in much of Europe and Asia, became more so this past year in the United States, after Hurricane Katrina kicked gasoline prices briefly to $3 per gallon.

Nowadays, two technologies are battling for the halo. In one corner stand Japanese and U.S. companies, which have invested billions of dollars in hybrid-electric technology. In the other corner are European makers, with decades of experience in light-duty diesel engines.

Today's hybrids cost so much to build that their fuel savings may not cover the higher sticker prices. They are most fuel-efficient in urban, stop-and-go traffic, and least economical at freeway speeds or under hard acceleration.

Diesels, on the other hand, tend to be dirty, and some of the air pollution standards they have to meet, such as those in California, are the world's strictest. Yet the will to make a clean diesel is there, because the engines are so fuel-thrifty. When DaimlerChrysler AG drove a diesel version of its Mercedes-Benz ML sport-utility vehicle and the similar-sized Lexus RX400h hybrid from New York City to San Francisco this past August, the diesel achieved 9.1 L/100 km (26 mpg), while the hybrid got 10.2 L/100 km (23 mpg). Still, diesels, too, come at a price: U.S. consumers, unlike Europeans, pay as much or more for diesel fuel as for gasoline.

Technology is blooming not just under the hood but in the passenger compartment as well. Carmakers are falling all over themselves to accommodate the ubiquitous Apple iPod in their stereo systems. BMW is building high-definition radio into its flagship 7 Series. Several manufacturers have integrated live feeds of traffic news into their navigation systems. The Mazda Sassou concept car forgoes an ignition key for firmware burned into a USB device. Fiat SpA announced that all its models will soon have USB ports to handle, well, who knows? A video game? Camera? Printer? The mind boggles.

Last year's single highest-tech car didn't have an iPod or an HD radio. In fact, it didn't even have a driver. In October, a bright blue Volkswagen Touareg sport-utility, nicknamed "Stanley," navigated itself through a treacherous, 211-km (131-mile) course in California's Mojave Desert in 6 hours, 54 minutes. By doing so, it captured for its creators a $2 million prize offered by the U.S. Defense Advanced Research Projects Agency, or DARPA, to promote the design of autonomous vehicles. Stanford University engineering students, helped by Volkswagen of America's Electronics Research Laboratory in Palo Alto, Calif., included a camera and laser sensors in Stanley that fed data to six Pentium computers, which handled the engine and the steering. On the side of the vehicle, the cheeky students actually rewrote Volkswagen's slogan, from "Drivers Wanted" to "Drivers Not Needed."

Don't look for self-driving cars in showrooms anytime soon. But do notice the small but significant milestones in that direction, such as the 2007 Lexus LS460 sedan, which will be able to park itself with minimal help from the person sitting in the driver's seat. Unlike the human driver, it can't be distracted by the iPod.

Concept Ford Reflex

A diesel hybrid that's both sporty and green

Building on the theme that "small is big," Ford Motor Co.'s highest-tech concept at January's influential Detroit Auto Show was a subcompact sports car. It was a tad unusual for a company that earns much of its North American profit from midsize, large, and very large trucks and sport-utilities.

The Reflex marries a small turbo-diesel, from Ford's European Fiesta, to a refined version of the hybrid-electric drive system used in its Escape Hybrid sport-utility.

The basic obstacle to using a conventional diesel engine in a hybrid-electric drivetrain is the fact that both the diesel and the electric motor typically have lots of torque at low revolutions per minute (around 1500 to 3000). Generally, you want a fossil-fuel engine that delivers peak torque at relatively high rpms, so that when you combine it with the electric motor you get a curve of overall torque versus rpms that is fairly flat. Ford's 1.4-liter turbocharged diesel engine fills the bill. It generates 41 kilowatts (55 horsepower) at 6000 rpm and 175 newton-meters (129 pound-feet) of torque at 4000 rpm.