With U.S. gas prices having fallen 40 percent over six months, fuel efficiency may be less important to car buyers than it was when gasoline cost $4 a gallon.
Meanwhile, smaller crossover utility vehicles are supplanting sedans and hatchbacks in more and more driveways.
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Added to an aging lineup of Prius models, those two factors may explain why Toyota's global sales of hybrid-electric vehicles actually fell 1 percent in 2014, to 1.27 million compared to 1.28 million the year before.
2000 Toyota Prius
Toyota is by far the world's largest producer of hybrid cars; it pioneered the technology in 1997 with the first Prius (sold only in Japan until 2000) and has now sold more than 7 million hybrids over 18 years.
The mainstay Prius Liftback was launched early in 2009 as a 2010 model, and remains almost unchanged. It is expected to be replaced with an all-new model late this year, using the next generation of Hybrid Synergy Drive.
Toyota added three additional members to the Prius family in 2012: a plug-in hybrid version of the Liftback, the Prius C subcompact hatchback, and the Prius V wagon.
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But while Toyota's 2014 hybrid sales were essentially flat, as reported last week by industry trade journal Ward's Auto, those of the second-largest producer soared.
Honda sold 284,000 hybrids last year, up more than 50 percent from its 2013 sales, which were almost entirely aging and smaller hybrid vehicles.
2014 Honda Accord Hybrid, Catskill Mountains, NY, Nov 2013
The 2014 sales increase for Honda reflects the launch of the well-received Accord Hybrid model, the first to use its new two-motor full hybrid system.
That technology reflects a shift in the U.S. market away from smaller hybrid vehicles--the Honda Insight has been withdrawn--based on the company's Integrated Motor Assist (IMA) mild-hybrid technology.
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Honda has replaced the IMA system with a new, stronger single-motor hybrid system in its latest Fit and HR-V subcompacts, but that system won't be offered in the U.S.
Instead, the company is adding the hybrid system to its larger vehicles. The Accord mid-size sedan is the first, and the company has hinted it will offer additional hybrid versions of larger products in future.
Ford, the world's third-highest producer of hybrids, sold 84,600 in 2014, a 1.7-percent decrease against the 86,000 it sold in 2013.