Toyota Estima Hybrid

Significant as it is, the Estima Hybrid is still too flawed to satisfy the mainstream public. However, by successfully implementing a four-wheel-drive layout, Toyota could have opened a whole new market for electrically powered off-roaders, while the Estima is bigger and more practical than any hybrid we've driven before.

How many engines does one car need? We've heard of bi-motor vehicles, but Toyota's latest environmentally friendly hybrid uses three powerplants to create the ultimate in green family transport.

By fitting its latest petrol/electric power system to the Previa - badged Estima in the home Japanese market - Toyota has given its hybrid technology much wider appeal. And, with a seven-seat layout and four-wheel drive, the car is practical. For the motorist, the Estima is as easy to drive as any people carrier with an auto gearbox - but it's much cleverer underneath.

The newcomer is fitted with a system similar to that of the Prius saloon, but here it incorporates a 131bhp 2.4-litre VVT-i petrol engine and a 17bhp electric unit to power the front wheels. Meanwhile, the rears are propelled exclusively by a 24bhp electric motor.

During normal driving, the petrol engine does all the work, but put your foot down and all three motors whir into life to provide maximum thrust. At urban speeds, the petrol powerplant cuts out entirely, and the two electric motors propel the car with zero emissions and in perfect silence.

Cornering control and stability are improved by activating the rear-wheel motor when it's needed. The battery is charged automatically, recycling energy normally wasted under braking, while an efficient CVT gearbox is the icing on the technological cake.

So it's very clever, but does it work in practice? Not quite. Acceleration is hard work, and the car is noticeably heavier than a normal MPV. The benefits in running costs aren't obvious, either - Toyota claims 50mpg, yet we managed little better than 25mpg as the petrol engine strained with the additional weight. The company won't be officially exporting this Estima to Europe, so it would be difficult for buyers to justify shipping in their own.

However, as the world's first four-wheel-drive hybrid, this is an important step in the shift to alternative power sources. Buyers will be making large sacrifices, but they can rest assured that they are driving the most efficient tri-powered car on the planet.