Road Test: Mercedes S400 is luxury with a conscience

Call it a guilt reducer for the rich or an honest effort to show that luxury and social responsibility aren't mutually exclusive: Two of the most expensive cars in America, the Lexus LS and the Mercedes-Benz S Class, are available as hybrids, for improved power and fuel economy.

The Lexus 600h L went on sale in August 2007; the Mercedes S400 arrived at U.S. dealerships in August as a 2010 model.

The Lexus packs 438 hp. from a V-8 engine and two electric motors and can scamper from zero to 60 mph in 5.5 seconds. The Mercedes has a V-6 and an electric motor making a total of 295 hp., and it takes 7.2 seconds to reach 60.

Both cars want premium gas. The Lexus is estimated by the Environmental Protection Agency at 20 miles per gallon in city driving, 22 on the highway. The S400's EPA estimates are a little better: 19 and 26.

Those aren't impressive if you're talking family cars - a four-cylinder Camry gets 22/33 - but they are for 17-foot gunboats weighing 4,800 pounds in the case of the Mercedes and more than 5,300 in the case of the Lexus.

My S400 tester's trip computer said I averaged in the mid to upper 20s on most trips I made during my four days with it.

The EPA says it costs $2,078 to drive the S400 hybrid 15,000 miles if gasoline is $2.91 a gallon. The cost of running a conventional V-8-powered S550, by comparison, is $2,427.

Obviously, the difference of less than $400 won't mean much to the rich. Nor are they likely to care much about the $1,150 federal tax credit available on this car.

But there are environmental considerations: The 550 uses 19 barrels of oil a year, says the EPA, while the 400 uses 16.3.

The Mercedes lists for "only" $87,950, compared with $107,300 for the Lexus.

No matter what the powertrain, the S Class, as anyone lucky enough to drive one of its models knows, is about as good as sedans get, at any price.

The S400 is roomy, almost eerily quiet, superbly comfortable, amazingly agile for its bulk if the suspension is switched to "sport." It's packed with safety and convenience technology organized so well I was able to operate every one of the many systems in the car except the navigation without referring to the owner's manual.

The SPEX
Vehicle tested: 2010 Mercedes-Benz S400 hybrid

Engine: 3.5-liter, 275-hp. V-6; 20-hp. magnetoelectric motor

Fuel:  Premium required

Transmission:  Seven-speed automatic, rear-wheel drive

Safety: Nine air bags; 4-wheel disc brakes with anti-lock, stability control, brake assist; Pre-Safe predictive accident preparation including up to 100 percent braking; Nightview Assist infrared road illumination; active suspension with crosswind stabilization; swiveling headlamps; cornering lamps; TeleAid telematics; fog lamps; daytime running lamps; tire pressure monitoring.

Place of assembly: Sindelfingen, Germany

Trunk: 19.8 cubic feet

EPA fuel economy estimates:19 mpg, city; 26, highway

Price as driven: $105,230 with freight

Bottom line: A green-tinted diamond