Think of the Lexus RX400h as an automotive superman. On the outside it’s Clark Kent — an ordinary-looking SUV, indistinguishable from a raft of Japanese and Korean models. But inside it has the power to save the planet.

At least that’s what the publicity claims. A sheaf of tables and statistics supplied by Lexus — the luxury offshoot of Toyota — claims it is the most fuel-efficient, environmentally friendly, greenest, leanest car of its kind.

That’s the kind of thing a motor manufacturer would say, of course. But it is true that some of the industry’s biggest players are staking their future on the hybrid power option that underpins this car. In Tokyo and Detroit, executives are already gearing up their companies to mass-produce hybrids.

In 10 years’ time — if the environmentalists haven’t shamed us all into riding bicycles, and if frugal diesels, the current vogue, fail to keep pace with ever-tightening environmental legislation — the new Lexus is probably the kind of car we’ll be driving. It will be in showrooms in Britain in July, with a price tag yet to be decided but likely to be in the region of £40,000.

Its fuel consumption is 32.8mpg combined, a very good figure for a big petrol-powered off-roader, and it has remarkably low carbon dioxide (a so-called greenhouse gas) emissions of 192g/km. That’s almost the same as a Ford Mondeo 2.0i, which has only half the power of the Lexus.



In fact Lexus reckons that an owner doing 14,000 miles a year in an RX400h will produce 2.6 tons less CO2 annually than somebody driving a similarly powered non-hybrid 4x4. Compare it with a diesel off-roader, though, and its advantages are less obvious. A BMW X5 3.0d will return 40.4mpg combined, although it will do only 24.8mpg around town compared with the Lexus’s 31.4mpg.

But what has Lexus had to sacrifice to achieve those figures? It’s hard to judge without driving it, and Lexus has made that difficult by keeping the car under wraps. I managed to get a sneak first drive but I had to fly halfway round the world to a deserted part of Hawaii to do it. Lexus was taking publicity photos and wanted palm trees, a rugged volcanic outcrop and as few onlookers as possible.

The RX400h is basically a re-engineered Lexus RX300, the model that has been around in Britain for five years. Externally, the car is almost indistinguishable from the 300 — just a couple more intake vents on the nose and, of course, different badging. Inside you’ll find a display much like the one in the Toyota Prius (another hybrid), which tells you when you’re being propelled by the petrol engine, when it’s battery power, and when it’s both.

It also lets you know when power is being captured and stored in the battery as the car coasts or brakes. It is a complex system, but as the reliable Prius seems to indicate, it should be pretty dependable in service.

Move off slowly, which the RX400h does with amazing smoothness, and you’ll be on battery power only. As your speed rises the engine joins in, but so seamlessly that you will struggle to identify the moment it happens.

As with the Prius, the RX400h uses a CVT (constantly variable transmission), which doesn’t have separate gears, so there are no kickdown or shift-point jerks. The result is a refined driving experience that rivals will be hard-pressed to match.

Then there is the performance: where the Prius feels pretty breathless most of the time, you really can feel the Lexus getting a helping hand from the electric motors. That’s especially noticeable in the midrange. The extra shove you get for overtaking from, say, 40 to 50mph feels more as if it’s from a V8 than the V6 it is. Pull out, put your foot down, and it seems as if the Lexus has magically drummed up an extra 100 lb ft of torque.

On Hawaii’s open roads the Lexus performed admirably, snaking round the clifftop hairpins and surging past the (very) slow local vehicles. It feels more agile than its bulk would suggest, and the huge amount of torque that is available across a wide rev range means it responds instantly to the throttle. This is definitely one of the more rewarding 4x4s to drive quickly on the road, although it isn’t the best — that remains the BMW X5.

Off-road, the Lexus is just as impressive. It cruised easily on the gravel roads that snake along the sides of the massive Mauna Loa mountain. On the loose gravel the RX400h performed well, with onboard computers calculating precisely how much torque to apportion to the front or rear wheels, depending on the grip available. In normal conditions the Lexus reverts to front-wheel drive only in order to conserve fuel.

The RX400h’s lusty 272bhp is helped by two powerful electric motors. I didn’t push it to its top speed, but Lexus’s test engineers let me try the RX400h on a drag strip. From a standing start the front tyres let out a loud chirp as the front end went light under acceleration, followed by a pretty relentless forward surge of acceleration. If anything, Lexus’s claimed performance of 0-62mph in 7.6sec seems conservative.

All of the other Lexus attributes are here in spades, too. The RX400h wafts along in leather and wood-bound luxury with the kind of equipment specification you expect of a luxury car. And the main cabin is spacious for four or five, although the Lexus is beaten on the practicality front by newcomers such as the Volvo XC90, which can take up to seven passengers.

As always, though, there’s a great big caveat attached to the RX400h experience. Drive a Prius with a heavy-ish foot and no thought about fuel economy and it will still give you a better-than-average return. I tried this approach with the Lexus and ended up getting, according to the trip computer, little more than 20mpg. When I quizzed a Lexus engineer about this, he said that you have to make a conscious decision as to whether you are going to drive for economy or performance. In a car that weighs nearly 220lb more than its non-hybrid sibling, it seems you cannot have both.

So the RX400h is good for the planet if you drive carefully. It’s also a good way of getting more performance while spending less on fuel, as long as you don’t use the performance that often.

Alternatively, you may take the view that, to save getting a headache weighing up the options, you’d have an easier life with a diesel off-roader.

WILL LEXUS CONVINCE THE ANTI-4x4 CAMPAIGNERS?

Blamed for everything from global warming to the war in Iraq, 4x4s have become the new pet hate of green campaigners. They have slapped spoof parking tickets on the windscreens of school-run mothers with such messages as “axles of evil” and “poor vehicle choice”.

Even the government is putting the boot in. Alun Michael, the rural affairs minister, is rushing legislation through parliament to limit off-roaders’ access to bridleways and similar routes.

Is the “environmentally unfriendly” tag deserved? Land Rover recently launched its new Discovery, for which the company claims an urban fuel consumption figure of 13.5mpg for the petrol model. Others, such as the Jeep Grand Cherokee V8 and Porsche Cayenne Turbo, are even thirstier, consuming 12.8 and 12.9mpg around town respectively.

By contrast, a small diesel hatchback such as Renault’s Clio 1.5 dCi will go a remarkable four times the distance of either of those on a gallon of fuel.

The new Lexus uses technology developed by its parent company Toyota, the world leader in hybrid technology. Batteries charged by its petrol engine drive electric motors to reduce fuel consumption. Toyota’s ultra-green, ultra-efficient Prius hybrid is European Car of the Year 2005, and by applying the same technology to its RX400h off-roader Lexus believes the 4x4 brigade can now have its cake and eat it.

It’s mean and green and its emissions are so low Lexus has applied for it to be exempted from the London congestion charge. Which means Mayor Ken Livingstone will hate it. A good reason to buy it?

VITAL STATISTICS

Model: Lexus RX400h
Engine type: V6, 3311cc petrol/electric hybrid
Power/Torque: 272bhp @ 5600rpm / 240 lb ft @ 1500rpm
Transmission: Continuously variable transmission
Fuel/CO2: 32.8mpg (combined) / 192g/km
Performance: 0-62mph: 7.6sec / Top speed: 125mph
Price: £40,000 (estimated)
Verdict: Refined, good to drive, with V8-style performance, but needs nurturing for real economy

THE OPPOSITION

Model: BMW X5 3.0d SE, £35,825
For: One of the best off-roaders to drive, great performance
Against: Appearance a bit dated, has an aggressive look

Model: Mercedes-Benz ML500, £45,290
For: Very spacious cabin with room for seven
Against: Not as good to drive as competitors, thirst for fuel