The only thing in common between trucks belching clouds of smelly black exhaust and the Mercedes-Benz GL320 CDI is the fuel they burn: diesel. This largish seven-passenger SUV has been to technology finishing school inside and out, and delivers an experience that sounds, feel, and smells like that of a gasoline-engine car—except that the GL320 CDI delivers fuel economy nearly 40 percent better than its gas-engine counterpart. Fill up and drive from New York City to Boston, then back, and your fuel tank still registers between a quarter and half full.

While the engine is efficient and fairly clean, this is not Mercedes' newest clean-diesel design, Bluetec, and it's not certified for sale in California, Maine, Massachusetts, New York or Vermont (though of course, you can legally drive through those states). The 3.2-liter V6 engine uses a turbocharger and seven-speed automatic to develop a seemingly modest 215 hp. But it still has plenty of performance, especially from a standstill, because diesels deliver lots of get-up-and-go torque—398 pound-feet at 1,400-2,800 rpm, for those who care. This from a vehicle weighing 5,296 pounds and measuring 200 inches long. While horsepower is the figure most people know, torque is what gives vehicles their get-up-and-go power. When a bulldozer pushes over a tree stump or the GL starts up smartly from a stoplight with a 7,500-pound boat and trailer in tow, that's torque talking.

Diesel technology works especially well in two diverse situations: idling and cross-country driving. When idling, a diesel engine uses much less fuel than a gasoline-powered vehicle does, which is good for taxicabs or long-haul truckers at rest stops. (But it's still not as efficient as, say, truckers hooking to AC power at a rest area, were that available.) On highways, diesel technology is more efficient than a gasoline engine and more efficient that a hybrid vehicle. Where a hybrid shines is in stop-and-go traffic, because regenerative braking recaptures the vehicles kinetic (motion) energy. But there's no reason that the engine paired with a hybrid couldn't be a diesel. Soon, it may be.

With my test GL320, the upshot was that on a long trip through New England, I managed about 25 miles per gallon cruising at 60 to 75 mph in a vehicle with a large frontal area shoving aside a lot of wind. With a comparable gasoline-engine SUV, such as the GL450 with a 335-hp V8, I would have been getting 17 or 18 mpg. There is an upfront price penalty for the sturdier diesel engine, though: about $1,000, over the gas-engine GL450. You could get the difference back in about 15,000 miles of highway driving at 25 mpg in a diesel car versus 18 mpg in a gasoline-engine vehicle, especially now that diesel sells for 10 to 30 cents a gallon less than regular and 25 to 50 cents a gallon less than premium.

All models—not just those with navigation—come with a center-console LCD and a pointing stick controller, called (collectively) the Comand system, for Cockpit Management and Data. Though the GL320 is fairly new, this is a previous-generation design with a glut of buttons, and it's hard to use. Some of the complexity of Comand may be why Mercedes-Benz's customer satisfaction score plummeted from fifth to 25th on the J.D. Power & Associates 2006 Initial Quality Survey, which gave more weight to such issues as usability and technical complexity. Newer vehicles such as the full-size S-Class and pending small (for a Mercedes, that is) C-Class use a less complex rotary knob. The cockpit itself is gorgeous, though, with hand-polished birdseye maple trim.

Here's why Comand is problematic: Thirty-seven buttons flank the Comand panel. A pointing-stick nub, like the TrackPoint button on a ThinkPad, only bigger, blacker, and wobblier, is on the far side of the display. The Comand pointer will be a difficult reach for any driver who doesn't scrape his knuckles when he walks. There's no wrist rest for the pointer, and even with Mercedes' air suspension, you'll be hard pressed to use it capably on all but glass-smooth highways. The press-to-select feature is especially difficult, because your fully extended arm salutes the dash at a 45-degree angle, but you're supposed to push straight back on this wobbly button.

Instead of a touchscreen, which German automakers abhor ("Ach! Think of the fingerprints!")—you make some selections with buttons angled in on the LCD frame. To tune to a radio or satellite radio station, you use a phonepad to the right of the display. This part makes sense once it's been explained, which it is somewhere in the manual, which total about 800 pages. The volume dial on the lower left of the Comand area barely juts out from the dash, so good luck adjusting the volume with gloves on, or if your fingers are greasy from that bag of potato chips you just consumed.

The last downside to the Comand structure is the steering-wheel buttons, which are nothing special, and not as advanced as the circular rocker switches on present-day Comand vehicles.

The color LCD is active matrix and recessed only modestly in the dash, so it washes out when the sun comes through a side window or reflects off your light-colored clothing. In a car this costly, Mercedes needs to think about using the costlier transflective displays pioneered by BMW in the X5 and 3 Series convertible: the more light shines off the display, the brighter it gets. And so does the rest of the auto industry, and the makers of portable navigation devices.

Because the display comes on all GL-class SUVs, both the diesel and the gas-engine version, that makes the navigation system option relatively affordable. And it can be installed by the dealer for $1,100 (versus $2,000 for similar systems on premium vehicles) or as part of a premium package with power seats, premium audio, Sirius satellite radio, power folding mirrors (essential in a vehicle this wide), parking sonar (Parktronic), a power tailgate, and to make the costs add up to an even $4,500, a cargo net.

Mercedes places a secondary display in the multifunction display in instrument panel between the speedometer and tachometer, where it provides some information, particularly rudimentary navigation arrows (nice if the main LCD is being used for something else). With audio choices, you often get some information, such as the satellite radio station playing, but not always the artist, song, or genre.

The GL comes with plenty of technology standard and more available but not cheap. The GL has all-wheel-drive (4Matic), and the transmission is a seven-speed automatic to improve fuel mileage. The standard air suspension (Airmatic) can increase ride height by 3 inches. Active cruise control (Distronic) runs $3,100; keyless go costs $1,100; a rear parking camera runs $500; and rear-seat entertainment goes for $2,650. These are all at the upper end of what's charged even in the premium segment.

Among audio offerings, Sirius satellite radio is part of $4,500 or $1,450 options packages, and an iPod adapter is a $365 upcharge. Mercedes-Benz doesn't yet offer HD radio, a hard drive for ripping CDs, or a PC Card socket for music-loaded flash cards. There is an auxiliary input jack, and that's free.

One of the most impressive aspects of a Mercedes is its crashworthiness. All seven seating positions get three-point harnesses. The side air curtains cover all three rows. The front passenger airbag inflates based on the passenger's size.

For those going a bit off-road, a hill-holder feature keeps the brake engaged for up to one second while you move your foot from brake to throttle, and there's a downhill speed regulation (DSR) to hold your speed at a crawl (3 to 10 mph) on steep hills, a one-button recalibration for off-roading, and an off-roading package for those going more seriously off-road—not just up their driveway at the ski chalet.

The GL320 suffers from a couple minor annoyances. The middle and rear cupholders lack depth, so water bottles are top-heavy and sports drink bottles barely fit the middle row and not at all in the rear. The backup camera lacks backing-assist lines. The electronic gearshift selector took me a bit of getting used to (make sure to press and hold the P-for-Park button, not just stab at it), though the electronic turn-signal indicator wasn't as tricky as BMW's. There's not a lot of storage space behind the third row of seats.

The GL is the largest of Mercedes' SUV line. It's costlier by about $10,000 than the ML SUV, which was vastly improved in its second generation by shedding its trucklike first-generation body, and the tall-wagon/crossover R-Class SUV, all of which can be had with the same V6 diesel as the GL320 or with gasoline powerplants. The BMW X5 and Acura MDX are more fun to drive, and BMW has a leg up on the GL—actually, on virtually every other vehicle out there—in technical sophistication, which is why it's our Digital Drive car of the year. The GL320 feels closest to the Lexus GX470 in its size and tall stance.

The GL, whether in its GL450 gasoline or GL320 CDI diesel format, is the better vehicle for 3 to 6 and maybe 7 occupants. Mercedes-Benz employs its 200 inches to good advantage: The third row of seats is actually usable by adults. It's 9 inches longer, and that translates into more spacious second and third row seating. Adults in the third row of the GL could actually manage a trip of an hour or two and not need chiropractic assistance at journey's end. Acura's third row is confining for adults, BMW's is even more cramped, and the Audi Q7's are a joke. I found the third row at least as comfortable as those of the Cadillac Escalade, Chevrolet Suburban, Chevrolet Tahoe and GMC Yukon, which are the same length as the GL320. Mercedes tuned the four-wheel-drive GL320 for comfortable cruising and hauling rather than sporty performance. Which is probably as it should be.

The Mercedes Web site has been spruced up for ease of navigation. Gone is the confusing model-selector grid that presented virtually every model and its list price on a single screen. Now you choose a model type, then read about features or go to the build-your-own screen. BYO is fairly straightforward, since Mercedes doesn't offer features in quite so many standalone combinations as arch-rival BMW. You may still be a bit confused in places, such as when ordering Bluetooth, as to whether the two options—$408 Bluetooth and the $220 Bluetooth cradle—are complementary, conflicting, or additive. (Answer: One provides the connection, the other provides recharging and docking.)

America is awash in SUVs. But the GL class may be in a field by itself: It's more comfortable and spacious than European competitors, with better hauling capabilities. It's better put together and handles better than even the new and vastly improved GM SUVs that represent the best from the U.S., and with a diesel option the Japanese SUVs don't have. Actually, since the GL comes from Alabama, it may be the best America has to offer even if we think of America as GM and Ford. And with diesel fuel selling for less than gasoline yet returning better mileage, diesel is the way to go with a Mercedes SUV. It's one clear way to economize, once you've plunked down $60,000 for the GL320 CDI.

Play Slide Show/All Shots (12)

$53,175.00 - $75,933.00

EPA rating: 20 city / 25 highway (diesel)

Near state-of-the-art diesel technology makes this seven-passenger luxury SUV relatively economical to run. Would that the Comand cockpit controller were as up-to-date.

Excellent fuel economy, no diesel smell or clatter inside, virtually none outside. Third row of seats actually holds adults.

Awkward previous-generation Comand dashboard controller with its glut of buttons. Turbo-diesel engine doesn?t meet emissions specs in five states (California, Maine, Massachusetts, New York or Vermont). Costly Bluetooth option.