LAFAYETTE, La. -- Dual two-lane bridges on concrete piers stretch bee-line straight for twenty miles or more across the cypress-studded and 'gator-infested Atchafalaya Basin swamp which sprawls to the east of Lafayette in southern Louisiana.
The long bridges form a section of I-10 called the Atchafalaya Swamp Freeway and due to the narrow lanes bound by concrete rails the speed limit drops to 60 mph for the seemingly endless length of swamp spans.
We're cruising across the Atchafalaya Swamp Freeway in a three-ton sport utility vehicle stretching 16 feet long and packing a four-wheel-drive (4WD) traction system plus a huge eight-cylinder engine which produces more than 330 hp.
To propel such a big-rig SUV down the pike at a quick clip with a muscular V8 normally consumes fuel best measured in mpb (miles-per-barrel) rather than mpg (miles-per-gallon).
But on this special SUV the dashboard trip computer's instant fuel consumption meter indicates we're burning 23.5 mpg along the swamp freeway.
Another meter reveals an average fuel score of 22.5 miles per gallon for the past 600 miles that we steered the big SUV while using a light touch to the right pedal.
What's our secret for achieving high fuel economy numbers with such a humongous and powerful SUV?
Well, you must understand that this SUV has been transformed into an hybrid electric vehicle (HEV).
General Motors constructs the HEV-SUV from the Cadillac Escalade, a truck-based sport utility wagon of the full-size and half-ton class that's the glitziest and most luxurious SUV on the road.
The HEV version of Escalade uses a special two-mode hybrid propulsion system developed by GM to trim the powertrain's fuel consumption and boost the economy ratings.
GM tests indicate that the Escalade Hybrid earns fuel economy figures up to 21 miles per gallon for highway runs in the two-wheel-drive (2WD) version, or up to 20 miles per gallon with the optional 4WD system.
And for in-town driving, the consumption numbers run to 20 mpg for the 2WD HEV-SUV as well as the 4WD version.
For such a large and powerful SUV these fuel economy scores are huge -- representing as much as a 50 percent improvement for city driving over a conventional Escalade with a 403 hp V8 aboard.
The conventional gas-burning 6.2-liter V8 in Escalade brings fuel economy numbers of 12 mpg for in-town driving and 19 mpg on the highway (2WD) or 18 mpg highway (4WD).
So there's some obvious savings to be earned from Escalade Hybrid's elevated fuel economy figures.
However, the front-end cost to add all of the hybrid equipment to Escalade amounts to almost $11,000.
GM sets the MSRP for a 2009 Escalade Hybrid at $71,900 (2WD) or $74,500 (4WD).
By comparison, the MSRP for a 2009 Escalade without hybrid equipment tallies to $60,900 (2WD) and $63,500 (4WD).
The HEV version of Escalade appears virtually identical to the conventional Escalde, save for strips of door decals denoting the hybrid nature and special "Hybrid 2 Mode" nameplates in chrome and green paint which decorate front fenders and the tailgate.
Dressed in high-gloss body paint and projecting a blunt in-your-face prow with shimmering chunks of chrome accenting a toothy grille, the 2009 Escalade Hybrid edition of Cadillac's full-size SUV rolls on enormous 22-inch wheels and carries a land yacht's collection of high-tech mechanical hardware as well as the trappings of an uber-luxury coach.
But the hybrid powertrain tucked inside this SUV's engine compartment is innovative and unusual.
First, there's the big 6.0-liter V8 engine aboard that drinks gasoline.
It knocks out 332 hp at 5100 rpm and high torque up to 367 lb-ft at 4100 rpm.
But the Escalade Hybrid SUV carries additional power sources -- namely, two 60-kW electric traction motors.
These electric motors are packaged with three planetary gearsets and four hydraulic wet clutches as components of GM's two-mode continuous electric ratio hybrid transmission, dubbed EVT for electrically variable transmission.
A high-tech HOS (hybrid optimizing system) control unit manages all energy produced by the on-board gas/electric engines and applies it directly to the SUV's wheels in infinitely variable measures, as well as providing four fixed-gear ratios so the operation mimics a conventional automatic transmission.
Power to run the two electric motors flows from a 300-volt nickel-metal hydride battery pack, the ESS (energy storage system) which is housed in Escalade's cabin below the second-row bench seat. The ESS also stores energy produced during regenerative braking and may be charged by the V8 engine with one of the electric motors used as a generator.
GM describes the high-tech apparatus for Escalade Hybrid as a two-mode hybrid propulsion system.
At low speed the wagon can move forward or backward using an electric motor or the gas-fired V8 or a combination of the V8 and electric motor.
At highway speed Escalade's second mode works with all eight cylinders of the gasoline engine pumping when commanded, or with only four cylinders firing through GM's AFM (active fuel management) technology to pare the number of cylinders in the combustion process and conserve on fuel.
And when the HEV-SUV stops, the V8 engine shuts down, leaving only electric motors running.
Although fuel economy scores increase with Escalade's hybrid treatment, the towing capacity decreases. GM rates the tow load for Escalade Hybrid at 5800 pounds (2WD) or 5600 pounds (4WD). By comparison, a conventional Escalade with the 6.2-liter V8 aboard can tow up to 8300 pounds (2WD) or 8100 pounds (4WD).
Escalade Hybrid has modifications to pare the body weight and improve aerodynamics. The prow dips slightly for aerodynamic efficiency, and the front hood and rear liftgate are made of aluminum to trim weight. Also, an electric power steering (EPS) system replaces an hydraulic apparatus.
A touch-screen video panel on the dashboard illustrates operations for the hybrid energy management system with icons representing the gas engine, electric motors, drive wheels and battery. Arrows depict energy flow from engine or motors to wheels and on to the battery for recharging.