2006 Mercury Mariner Hybrid 4WD
Like Toyota's hybrids, the Mariner can accelerate from a dead stop using electric power alone. Caught in rush-hour traffic,

Alt Fuel: Biodiesel

Optimists Say: Since B20, which is 20 percent biodiesel made from refined (or recycled) vegetable or soybean oil, can be pumped straight into diesel cars, it's the only alternative fuel that doesn't require an upgrade to a new ride. Better still, it reduces emissions by 50 percent compared with petroleum diesel. Thanks to a 2005 federal tax incentive for biodiesel blenders, its annual use is expected to double in 2006 to 150 million gallons in the U.S. Pessimists Say: That's still just a drop in the bucket, and B100 (100 percent biodiesel, an option for newer diesel cars) gums up in cold weather. Learn More: www.biodiesel.org —M. M.

I found myself cheering for the system as it kept the vehicle rolling along soundlessly at speeds of up to 30 mph. The Mariner shares its architecture and engine (and parent company) with the Ford Escape Hybrid, though a few suspension tweaks give the Mariner a more supple ride. All bets are off when road surfaces get overly rough, however; engineers can only go so far to make an SUV glide like a town car. Between the electric motor and its 2.3-liter four-cylinder gas engine, the Mariner offers a sincere amount of oomph from the start, but highway passing is tedious and towing capacity is a feeble 1,000 pounds. The passenger room is spacious, and a large cargo area gives the Mariner a leg up on both gear-laden road trips and Saturdays in suburbia.

MSRP: $29,840 As tested: $33,635 Hybrid premium: $5,000 MPG: EPA, 32 city/29 highway; our average, 24 Decrease in annual greenhouse-gas emissions from comparable gas-only model: 26.8 percent Pros: Road feel, cargo space Cons: Engine noise, mileage just adequate