Five finalists for Green Car of the Year

Volkswagen's highly anticipated Jetta TDI is the the first 50-state-compliant clean diesel.

At first glance, this seems like a regular Jetta that runs on regular gasoline, but there's a surprise under the hood. This Volkswagen Jetta TDI is America's first 50-state-compliant clean diesel.

The EPA estimates the Jetta TDI gets 29 mpg city and 40 mpg highway, but independent testing has yielded numbers as high as 38 mpg in the city and 44 mpg on the highway.

The Guinness World Record for fuel economy around the country was set by John and Helen Taylor in a VW Jetta TDI. The couple averaged 58.82 US mpg over 20 days, 48 states, and 9,419 miles.

Equipped with the BMW Advanced Diesel with BluePerformance, the 335d Sedan is set to be unveiled at the 2008 Detroit Auto Show alongside the the X5 xDrive35d, but the Green Car of the Year nomination may cause BMW to bump it up.

The 335d Sedan is powered by a 3-liter turbodiesel that uses two turbochargers in series. At low speeds, a small turbocharger is able to spin up quickly, and without lag. As the engine gains speed, a larger turbo comes online, taking over for the small turbo.

Thanks to the efficiency boosting turbos, the 335d is expected to produce a maximum output of 265 hp and peak torque of 425 lb-ft and 23 city and 33 highway mpg on low-sulfur diesel fuel.

The 335d uses a urea injection system called AdBlue to clean exhaust fumes of nitric oxides by way of chemical reaction.

The Smart ForTwo is a game changer. It challenges the notions of what a vehicle is supposed to be and do with its tiny form factor and thrifty engine.

It doesn't take much power to motivate a tiny two-seater such as the Smart ForTwo. Its 1.0-liter, three-cylinder engine outputs a mere 70 horsepower. The ForTwo hums along to the tune of 33 city and 41 highway mpg, with equally stringent emissions.

Available in three trims--pure, passion, and cabriolet--the ForTwo is an odd little vehicle that attracts stares and questions where ever it goes.

The EPA has put the smart ForTwo at the top of its current list of the most economical cars without hybrid drive. The US authority confirms independent European studies that had already established the clever two-seater as the most economical car.

The all-new 2009 Saturn Vue Hybrid uses General Motors' Two-Mode Hybrid, which we've seen on the GMC Yukon Hybrid. The Vue is unique because it is the first front-wheel-drive application of the system.

The Vue 2 Mode Hybrid is expected to deliver an estimated 50-percent fuel economy increase over the nonhybrid V-6 Vue XR. It also is expected to have a driving range of more than 500 miles.

The combination of a 3.5-liter gasoline V-6 and an electric motor makes for a maximum 255 horsepower and 252 pound-feet of torque.

In the first mode, at lower speed and lighter loads the Vue 2 Mode Hybrid operates in one of three ways depending on conditions and battery charge level: all-electric power, internal combustion engine power, or a combination of the two. All reverse operation is driven solely by the electric motors.

The second mode is used primarily to optimize fuel economy at highway speeds to optimize fuel economy. It provides electric assist in addition to six-cylinder power when conditions demand it, such as trailer towing and climbing steep grades, and to allow the engine to run at its most efficient point under less demanding conditions.

The Ford Fusion Hybrid (and Mercury Milan Hybrid) utilizes technology similar to what we've seen on the Ford Escape and Mercury Mariner. The Fusion will have an expected range of 700 miles of city driving on a single tank and the ability to operate in purely electric mode at speed of up to 47 mph, thanks to a smaller, lighter battery.