Roughly one in five Lexus RX crossover SUVs sold is a hybrid, and with the debut of the third-generation RX -the second-generation RX hybrid -company officials expect that percentage to remain about the same. Overall, the new RX represents a careful evolu­tion of what is, after all, the brand’s most popular model, and the hybrid model com­mendably moves a bit more in the direction of fuel efficiency.

Lexus engineers describe the brand’s hybrid philosophy as standing on four pillars: per­formance; refinement; quiet, low emissions; and fuel economy. Lexus has been criti­cized that its hybrid models emphasize the first pillar too strongly – Lexus hybrid mod­els are typically the fastest and most powerful version in the lineup -and therefore underachieving in the last pillar, which arguably is the quality that’s most important to hybrid buyers.

While the architects of the new, 2010 Lexus RX still maintain the importance of all four pillars, we’re happy to report that it is fuel economy that has made the biggest advancement over the outgoing car. The front-wheel-drive Lexus RX is up by 1 mpg city and 3 mpg highway, to 28 mpg city, 27 mpg highway. With all-wheel drive, the increase is 2 mpg city and 2 mpg highway, to 28 mpg city, 26 mpg highway.

Whereas the standard RX350’s engine is little changed, the RX450h got a whole new gasoline engine. The 3.5-liter V-6 is an Atkinson-cycle powerplant, which is a highly efficient variant on the internal combustion theme, but one that’s rarely seen. (Its best-known ap­plication was in the 1993-2003 Mazda Millenia S.)

The engine, while economical, doesn’t produce much in the way of low-end torque, but that actually dovetails well with the elec­tric motors in a hybrid application, because electric motors make their maximum torque at the very bottom of their rev range. Here, the combo puts out 295 hp, which again makes the hybrid the most powerful RX and produces strong, seamless acceleration.

As in most hybrids, however, there is a faint surging as the power-train switches between draining and recharging the batteries dur­ing steady-state driving on flat roads. In all-wheel-drive models, the rear wheels are driven only by an electric motor-generator; there is no driveshaft running from the gasoline engine to the rear wheels.

Outside of its powertrain, the redesigned RX400h, like the RX350, is treated to sev­eral bits of new technology. The optional rear-view camera (now available with or without purchasing the navigation system) can be supplemented with a curb-view camera, which is mounted in the right-side mirror, to help with parallel parking.

The navigation system boasts new features, like XM NavTraffic and weather, and is controlled by a new mouse-type controller. It looks like an iDrive-style device but works like a joystick, with several surrounding buttons with dedicated functions. There’s also an available heads-up display, automatic high beams, and remote start.

As before, the RX400h interior is plush and comfortable. The exterior is a refine­ment of the shape introduced with the previous generation. Even with the new car’s higher fuel economy, buying the hybrid is a decision made more for love (of effi­ciency and the environment) than money (saved at the gas pump).