Soaring fuel prices have spurred US demand for hybrid petrol-electric vehicles. Sales of the Toyota Prius, the top-selling hybrid, reached 9,850 in August, more than double a year earlier. Toyota has sold 72,849 Priuses this year, up from 31,406 in January-August 2004.
Sales of Honda's smaller Civic hybrid more than trebled in August. Ford sold almost 1,400 petrol-electric versions of its Escape SUV even though it didn't qualify for employee discounts available on most other models.
Hybrids made up 1.6 per cent of total US light vehicle sales last month. But, according to a survey by CNW Marketing Research, almost a third of respondents said they would consider buying a hybrid, quadruple the number in July.
General Motors, which introduced hybrids of its Chevrolet Silverado and GMC Sierra pick-up trucks last September, said: "We're selling every one we build." It declined to disclose sales.
Hybrids are most effective for city driving, where the electric motor is sufficient for propulsion and no petrol is wasted when the vehicle is idling.
David Champion, director of auto testing at Consumer Reports, estimates that, at current fuel prices, a Prius saves about $530 on petrol a year compared with a similarly-sized Toyota Corolla. At that rate, it would take about 10 years to recoup the price difference between the two cars.
The trade-in value of an 8-10 year-old Prius is also uncertain. "If you want to do your bit for the environment, a hybrid really makes sense," said Champion. "If you're looking at them purely as a financial solution, the payback is long."
Questions have also been raised about some hybrid fuel economy. A New York Times review of Toyota's Lexus RX400 SUV concluded: "Toyota's motivation in pushing hybrid technology may turn out to be a different shade of green than we've been led to believe, one much closer to the colour of money." Toyota sold 2,607 Lexus hybrids last month. Toyota plans to introduce 10 new hybrids worldwide by early next decade, and projects that hybrids will then account for a quarter of its US sales, or 600,000 vehicles a year.
GM and DaimlerChrysler are collaborating on a technology that replaces a conventional automatic transmission with a dual-mode mechanism, requiring a smaller electric motor and battery.