We've spent most of our time here at AllAboutPrius.com writing about the new 2010 Toyota Prius, for (LOL) pretty obvious reasons. But while that car's Hybrid Synergy Drive system is used in other Toyota models, the Prius has been its sole "dedicated hybrid".

Now the company has launched a second hybrid-only vehicle. But this one's for Lexus, its luxury marque. The 2010 Lexus HS250h shares the hybrid system and a wheelbase with the 2010 Toyota Prius, but visually and experientially, it's a very different car.

For one thing, it's not a hatchback like the Prius but a more conventional four-door sedan with a trunk. (It does have little triangular side windows ahead of the front doors, though, just like the Prius.)

The HS also has a bigger engine with more horsepower: 2.4 liters and 147 horsepower, versus 1.8 liters and 98 hp. That reflects a different tradeoff between ultra-high fuel economy and the silent, smooth, luxurious driving experience Lexus is known for.

Now our colleague Bengt Halvorson has gotten our first drive of this eagerly awaited new hybrid. For AllAboutPrius readers, the first question may be: So, how's the mileage?

Well, says Bengt, the news is mixed. The EPA ratings are 35 miles per gallon city / 34 mpg highway. That isn't as high as the 51 mpg city / 48 mpg highway figures returned by the 2010 Toyota Prius (though keep in mind the difference is just one gallon of gas every 100 miles).

But Bengt got mileage below the EPA numbers in mixed traffic at the Orange County, California, preview. The HS250h returned 30 mpg in mixed traffic, and as little as 22 mpg on a route with many hills.

On the high end, though, he was able to stretch gas mileage to 46 mpg in "exceptionally gentle, controlled conditions on level roads". And that number is within spitting distance of even the latest 2010 Toyota Prius.

It's all because the added layer of Lexus luxe adds something else, too: weight. In other words, the 2010 Lexus HS250h needs more energy (for which read gasoline) to move itself down the road. Compared to the 2010 Prius, it's a jaw-dropping 600 pounds heavier.

Combined with the bigger engine--for a quicker time from 0 to 60 mph of 8.4 seconds, says Lexus--it's not surprising the mileage is lower.

But there's good news too: It's a much nicer car. "The 2010 Lexus HS 250h is tight and quiet inside," says Bengt, "thanks to details like an acoustic windshield and triple-layer door seals," although "coarse engine noise makes itself known under acceleration."

Then Bengt succumbed to the lure of the Lexus luxury experience. "Our indifference about the driving experience was replaced by gadget lust," he said, without a hint of shame. "The HS 250h has enough of the latest tech features to rival all but the brand’s LS 600h flagship."

We'll report more on those features, as well as the price--when Lexus reveals it--later this year. We hope to drive the car soon, and will bring you a special AllAboutPrius.com road test when we do.

And now, we return you to our regular programming: the 2010 Toyota Prius.

2009 Detroit auto show

2009 Detroit auto show