The Toyota Prius hybrid, once viewed as a science experiment for environmentalists, has become a mainstream vehicle in the United States, with the company selling more than a million nationwide.Toyota announced the milestone as fuel prices worldwide continued to rise. The Prius, powered by a petrol engine and an electric motor, gets an estimated 22km/litre in city driving and, aside from electric vehicles, is the most fuel-efficient car in the US, according to the Environmental Protection Agency."Prius paved the way for hybrids," Bob Carter, Toyota Division group vice-president and general manager in the US, said in a statement.TOTAL TOPS THREE-MILLIONToyota began selling the Prius 11 years ago when fuel prices were low. At first it was a car for the environmentally conscious but, as prices spiked during the decade, its popularity increased. In the first quarter of 2011 Toyota already has sold nearly 43 000, 52 percent more than at the same time in 2010, according to Autodata. In 2010, the company sold more than 140 000.Prius sales worldwide topped two-million in 2010 and Toyota said its total global hybrid vehicle sales now exceed three-million."Prius has become synonymous with the word hybrid," Carter added. "It has accounted for more than 60 percent of hybrid-car sales so far in 2011."PRODUCTION RE-STARTEDSome Toyota dealers have been reporting that Priuses are in now in short supply because of high demand and factory outages in Japan due to the March 11 earthquakes.The quakes and tsunamis forced Toyota to stop production at most Japanese factories but the company restarted two plants that make Prius and Lexus on March 28.Moody's Investors Service has warned that it might have to downgrade TMC's credit rating due to the financial fallout from suspended production.