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In April, Lexus introduced the 2006 RX 400h, the world's first gas/electric hybrid-powered luxury sport-utility. Based on the RX 330, the RX 400h does the impossible: It delivers better performance, better fuel efficiency and significantly reduced emissions while sacrificing none of the RX 330's luxury or utility.

Toyota, which manufactures the Lexus, has been in the forefront of hybrid technology and now has a wide range of hybrid vehicles on the market spanning the Toyota and Lexus model ranges. The RX 400h is the first true luxury vehicle from any manufacturer to be so equipped and it proved to be a fascinating road test from several perspectives.

The RX 400h incorporates a new, advanced Hybrid Synergy Drive system that combines the 3.3-liter V6 engine of the RX 330 with a high-torque electric drive motor-generator, plus a rear electric drive motor-generator to provide on-road all-wheel drive capability. With a combined system output of approximately 268 horsepower, the RX 400h delivers sprightly acceleration with surprisingly high fuel efficiency. At 7.3 seconds, acceleration from zero to 60 mph is better than many V8-powered competitors. And the RX 400h actually delivers better fuel economy in town than it does on the highway.

All conventionally-powered vehicles offer better fuel economy on the highway. Even though you are using more fuel at 65 mph than you are at 30 mph around town, urban driving involves lots of dead time when you're sitting at stop lights, stuck in traffic, etc. At that point, your engine is chugging away at idle using up gasoline that delivers no benefit at all, and killing your fuel economy in the process. With a hybrid, the engine quits when the vehicle comes to a stop, while the electric motor kicks in to provide the juice required to keep the accessories, lights, etc., functioning. Then, when the throttle is engaged, the engine is restarted and the electric motor is feathered. In the RX 400h, the transition from engine to electric motor and back to engine again is utterly seamless.

In addition to all of the above, the RX 400h features an electronically-controlled and continuously-variable transmission. In practice, that means gearshifts that you never feel. The RX 400h is, in short, remarkably smooth in its operation, whether accelerating, decelerating or standing still.To say that Lexus engineers have done a good job here would be an understatement.

The RX 400h is defined as a "full hybrid," too, which means that it is capable of operating in electric-only or gas engine-only mode as well as a mode that combines the power of the gas engine and electric motor. In contrast, other hybrid technologies are not capable of running only on electrical power, but instead require constant gas engine operation.

Externally, the RX 400h differs in subtle ways from the RX 330. The RX 400h features a revised grille, a new front fascia with additional air intake, sporty round foglamps, unique 18-inch alloy wheels and Light Emitting Diode (LED) tail lamps. Inside, brushed aluminum accents replace wood trim, and a power meter replaces the tachometer. The RX 400h also includes struts with internal rebound springs and linear control valves and features specific suspension tuning for sportier handling.

Inside, all of the comfort and luxury found in the RX 330 is present in the RX 400h, with a few minor differences: The brushed-aluminum accents lend a contemporary look and the view of the instruments has evolved: In place of a traditional tachometer, the RX 400h has an illuminated power meter that displays the level of power generated by the hybrid powertrain. The driver can also monitor the gas-electric power distribution on the multi-information display or on the optional navigation system's seven-inch touch panel display screen. The large rear cargo capacity of approximately 38 cu. ft. expands to nearly 84 cu. ft. with the rear seatbacks folded down.

The RX 400h carries a base price of $48,535, plus $650 in destination charges. Our test vehicle had four grand in optional equipment for a final sticker of $52,703. The options included a DVD rear entertainment system ($1,840), heated front seats ($540), the top-end Mark Levinson sound system ($980), and a few inexpensive doodads that don't bear mentioning.

In sum, we liked the Lexus RX 400h a lot. It's a fully competitive luxury vehicle and environmentally friendly at the same time. If you've got fifty grand to spend on a set of wheels, you couldn't do much better than the RX 400h and you could do a whole lot worse. R&D