Audi and BMW are out to prove that "fun-to-drive" and "extremely low emissions" are not mutually exclusive concepts. This week at the Frankfurt Motor Show the German automakers are showing sexy concept cars that caught our interest even before we learned about their futuristic powertrains.

The concept cars -- the Audi e-tron and the BMW Vision EfficientDynamics -- feature low emissions yet accelerate from 0-62 mph in 4.8 seconds, more than twice as fast as a Toyota Prius, according to Motor Trend magazine. The concepts demonstrate how premium automakers like Audi and BMW will retain the values that make their cars successful while still meeting increasingly stringent fuel efficiency standards around the world.

BMW's concept is the Vision EfficientDynamics, a car that is infinitely more interesting than its name suggests. The bold BMW is a full hybrid, meaning it can function on electric and diesel power working together or independently. Unlike all hybrids sold in the U.S., this one has a diesel engine instead of gas. The three-cylinder turbodiesel engine contributes to better fuel economy and provides additional torque than would probably be possible with a gas engine. Oh, and did we mention the four-seater has gullwing doors?

The two electric motors are positioned on the front and rear axle, keeping the concept's weight distribution relatively balanced, which is important for handling. Driven carefully, the Vision EfficientDynamics can go 31 miles, or from USC to that other major school in Los Angeles and back with a few miles to spare, all on electric power. On the way, the 351-horsepower vehicle will slip through the air with a drag coefficient of 0.22 (that swoopy styling is not just for show) and use its Brake Energy Regeneration, which stores energy in 98 lithium polymer cells. If you reach the BMW's electronically limited 155-mph top speed, don't count on hitting the fuel economy rating of about 63 mpg measured by U.S. standards.

Audi's e-tron concept (who develops these names?) looks more down-to-earth than the BMW concept but no less slick. That's because the Audi e-tron closely resembles the automaker's flagship R8 sports car. Like the BMW, the Audi is all-wheel drive. Four motors, two each at the front and rear axles, propel the car. You'll get from USC to the California-Mexico border before needing to recharge this all-electric vehicle. 

The lithium-ion battery sits just behind the two seats -- good for weight distribution and, in turn, handling. While the e-tron has a healthy 308 horsepower, its 3,319 lb-ft of torque is mind-boggling. Audi says the car can send as much torque as needed from the four electric motors to the wheels.

The concept is equipped with a technology called "car-to-x communication" that can connect with vehicles, traffic lights, or even parking structures. Think of it: you enter The Grove's parking structure and, with this technology, your car finds and reserves a spot. Or, the car might use navigational data about traffic flow on the I-10 to prevent the driver from using excessive energy. "Car-to-x communication" systems like this, however, require every vehicle on the road to have the technology, meaning it's unlikely you'll see it on a car in a dealership soon. 

That's not necessarily true for the basic powertrain technology at the heart of the Audi and BMW concepts. With price-unlimited concepts, it's much easier to explore gee-whiz technology that might eventually appear on a production vehicle. The challenge now is for automakers to engineer a somewhat affordable production vehicle -- whether it be a diesel hybrid or fully electric -- that's easy on the environment and enjoyable on a winding road like Mulholland Drive.