UCS updates its hybrid scorecard, praises Mercedes S400, slams BMW X6

2010 Mercedes-Benz S400 Hybrid – Click above for high-res image gallery

A couple of months ago, the Union of Concerned Scientists (UCS) first published its hybrid scorecard. That hybrid value reference source has now been updated with two newly available luxury models. UCS has used the Mercedes-Benz S400 hybrid and BMW X6 Activehybrid to illustrate what automakers have done right and wrong with hybrids.

The Mercedes replaces the V8 engine of the S550 with a smaller V6 engine when paired with its mild hybrid. Mercedes also doesn't tack on any extra mandatory equipment to inflate the already steep price. The result is a comparative value, with the S400 being the least expensive S-Class offered in the U.S. market.

By way of comparison, the X6 pairs the even more powerful 455 horsepower of the V8 engine found in conventional models with the two-mode hybrid system. Features like premium audio and other standard equipment add an extra $10,000 to the price tag. While the X6 gets a better fuel economy rating than the non-hybrid models (barely) the high-cost doesn't seem justified. UCS would prefer to see hybrid systems paired with smaller engines for even better efficiency and lower cost so that more people can afford them.

X6 Photos copyright ©2009 Sebastian Blanco / Weblogs, Inc.
S400 Photos Copyright ©2010 Sam Abuelsamid / Weblogs, Inc.



WASHINGTON (April 12, 2010) - In the first update to their Hybrid Scorecard, auto engineers at the Union of Concerned Scientists (UCS) found that the BMW ActiveHybrid X6 squanders its hybrid drivetrain on boosting power, while the Mercedes-Benz S400 hybrid achieves some success in lowering costs by combining its relatively weak hybrid drivetrain with a downsized conventional gasoline engine.

BMW's first hybrid, the luxury ActiveHybrid X6 is a "muscle hybrid." BMW layered the car's hybrid drivetrain on an already powerful eight-cylinder engine to boost performance, giving it the highest horsepower and torque of any hybrid on the market. By contrast, the new Mercedes-Benz S400 Hybrid, also the company's first hybrid, went from an eight-cylinder to six-cylinder engine compared with its base model.

Downsizing the S400's engine provided significant cost savings and the bulk of its fuel economy improvement over the conventional S550. The S400 Hybrid actually costs less than the S550, a first for a hybrid. The S400 Hybrid is a mild hybrid, which means that its gasoline engine idles when the vehicle stops and it has regenerative breaking, but the vehicle cannot run on electric power alone. Notably, it is the first production hybrid that uses lithium-ion batteries, which provide greater energy storage per pound than conventional batteries.

Despite its hybrid label, the BMW ActiveHybrid X6 performs far worse from an environmental perspective than the only other midsize luxury hybrid SUV on the market, the Lexus RX 450h. UCS gave the X6 a low environmental score of 4.4 out of 10, but gave the RX450h a 7.4 rating.

The X6 comes with $10,000 of "forced features," including a deluxe sound system and other features not included in its base model. The S400, conversely, has no forced features compared with its base model. While both cars are already quite expensive luxury vehicles, UCS's initial Hybrid Scorecard analysis found that forced features unnecessarily drive up the cost of hybrid cars across vehicles classes.

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