A new breed of SUV will be rolling out this fall. They will be big, powerful and half electric.

It was an age-old story of forbidden love, destined to repeat itself. For years they would pass one another on the road, exchange glances across the intersection, and fantasize about the possibilities. Everyone said they should be sworn enemies but the attraction was undeniable. It was just a matter of time, really.
This fall, the full-size SUV and the hybrid will have their first offspring, and they'll be burly ones: a Chevrolet Tahoe and a GMC Yukon. But they won't be alone for long. Not only is General Motors expecting a full hybrid version of the Escalade, Sierra, and Silverado 1500, but DaimlerChrysler will soon be delivering a hybrid Dodge Durango and Chrysler Aspen. The age of the monster hybrid is now upon us.

The new breed is quite a bit different from its smaller hybrid SUV competitors: the Toyota Highlander Hybrid, Lexus RX 400h, Mercury Mariner Hybrid, Ford Escape Hybrid, and Saturn Vue Green Line. GM and DaimlerChrysler, the two carmakers leading the charge, will use a technology they co-developed along with the BMW Group called the Two-Mode hybrid system, specially designed for big vehicles.

Both companies say that their full-size SUV hybrid models will be up to 25 percent more fuel-efficient, putting them in the ballpark of 20 miles per gallon combined city and highway.

The arrival of the full-size hybrid SUV is sure to be a touchy subject. The debate over the merits of these "green giants" will fall into two camps. For some it will be a step in the right direction: Since Americans are going to buy SUVs, they ought to have a hybrid option. It will also make the notion of hybrid cars more palatable to a wider audience, especially for drivers who might roll their eyes at a Prius.

The other camp will argue it is a case of greenwashing that makes a mockery of the hybrid name. Rather than making SUVs considerably more efficient, as Detroit had the opportunity to do, the industry is making the battery and electric motor into a performance-boosting extra. Or worse, these "muscle hybrids" might now appeal to drivers who previously felt guilty for wanting an SUV, which could lead to more oil use, not less.

There certainly is evidence from the last decade that when choosing between upping performance or improving fuel economy, the auto industry has applied technological advances to make its ever-larger cars faster rather than more efficient. Between 1984 and 2002, the average car grew 20 percent heavier and gained 25 percent better acceleration while miles per gallon stood still. Critics say that Detroit is using hybrid technology as a way to give SUVs yet more power, plus put a spit shine on the SUV's fading reputation.

The fact is, General Motors isn't slacking in the engineering department. While Ford struggled to develop a hybrid system to compete with Toyota's Synergy Drive (and in the end licensed technology from the Japanese maker), the Two-Mode hybrid system appears to be a legitimately innovative contribution. It is not a mild hybrid system like the one now appearing in the Saturn Vue Green Line, but a series hybrid like the Prius, with some unique features.

Based on GM's technology for hybrid transit buses, the Two-Mode system is well-suited to the special needs of larger, heavier vehicles. DaimlerChrysler, General Motors, and the BMW Group joined up in 2004 to further develop the technology for use in larger SUVs, and now have a joint development center in Troy, Mich.

With two electric motors, four clutches, four fixed gears, and three planetary gear sets, the upshot is that the new hybrid system has two distinct modes that boost power and efficiency at low and high speeds. This allows for more efficient cruising, heavy towing and hill climbing. The hybrid system is also paired with the Multi-Displacement System (MDS) that puts cylinders to sleep when not needed.

While the technology of the Two-Mode may be impressive, drivers may be less awed by the gas mileage. A non-hybrid Dodge Durango with a 4.7-liter V8 engine will get about 14 mpg combined city/highway. A hybrid Durango with the same engine may get just four or five more miles to the gallon. The 5.7-liter HEMI V8 version will almost definitely be lower still.

Compare this with the smaller Ford Escape: Adding the hybrid system gave the Escape a modest boost of eight miles per gallon, bringing it up to a combined average of around 30. The Escape and the Durango are certainly different beasts, but the real question may be, is a hybrid Durango a different enough beast from the standard model to woo drivers?

But there may be some interesting and unexpected benefits that come with the birth of the mega-SUV. With so much talk of biofuels and hybrids, it is surprising we haven't yet seen the two combined. Ford has an E85 flex-fuel hybrid Escape that is a research vehicle, but nothing has hit the market yet. Dodge, however, has announced that it will offer a flex-fuel Durango hybrid with its 4.7-liter Magnum V8, and the Chrysler Aspen hybrid may also come in an ethanol option.

Another feature that could wind up being quite significant is that the four-wheel regenerative braking system of the Two-Mode hybrid is reported to make braking much more responsive. Drivers love SUVs for what they perceive to be greater safety, but studies have found that while many SUVs are safer in crashes than smaller vehicles, they are also more likely to get into accidents, partly due to soggy braking. The more perky performance of the new regenerative brakes may prove to actually make SUVs safer, both for their drivers and for cars such as the Honda Fit and the two-seat smart car.

While it may be inevitable that full-size SUVs go hybrid, it remains to be seen whether drivers will desire them. While hybrids show strong sales, America's largest SUVs are now a suffering species. The Ford Explorer, long the best-selling SUV in America, recently handed that crown to the smaller and more fuel-efficient Honda CR-V. Joseph White of the Wall Street Journal is calling it "the great SUV die off," and likens their decline to the effect of a certain asteroid on the dinosaurs. Presumably, American companies have done their homework and feel confident that customers are going to want a hybrid HEMI Durango.

GM still hasn't announced what the price tag of the hybrid Tahoe and Yukon will look like, but it is already being reported that the company may absorb some of the higher cost to make this new breed more attractive. With the arrival of the "green giants" this fall, there will be much discussion of where the hybrid movement is headed. But ultimately, their fate will depend on how many people will step up and buy one.

Jacob Gordon is a freelance writer, a blogger for TreeHugger.com, and producer of TreeHugger Radio. He can be reached at by jacob@treehugger.com.

help from the electric motors would ensure that the load was low enough that AFM could be activated for cruising at any speed