President Obama's goal of having 1 million plug-in hybrid-electric vehicles on U.S. roads by 2015 may be too lofty, says a top Toyota official.

“It's a big, big challenge,” Josephine Cooper, group vice president-government affairs for Toyota Motor North America Inc., says at the Management Briefing Seminars, an annual industry gathering in Traverse City, MI.

Cooper notes standard HEVs have been available for 12 years (first-generation Toyota Prius and Honda Insight), but in 2009 they make up just 2% of the total U.S. new-vehicle market.

With current sales volumes, Obama's goal amounts to 10% of all vehicle sales.

“Five years will be a challenge, and I'm not sure we'll be able to make it,” she says of the 2015 plug-in target.

Nevertheless, Toyota will aggressively pursue the goal and plans to debut a plug-in version of the Prius for fleets later this year in the U.S, she says.

But she notes groups and individuals that have used aftermarket plug-in conversion kits to make their standard HEV a plug-in have seen fuel economy that hasn't lived up to the hype.

“We have heard claims of more than 100 mpg (2.4 L/100 km)” from third-party conversion proponents, Cooper says.

But fleet customers such as the U.S. Department of Energy “are averaging less than 55 mpg (4.3 L/100 km) in real-world driving conditions,” with unproven battery technology.

Echoing comments from Nissan North America Inc.'s Larry Dominique, Cooper says introducing vehicles that don't meet consumer expectations could hurt the industry and hinder public acceptance of advanced powertrain technology.

“That would set us all back a long, long way,” she says.

Cooper restates Toyota's longstanding position to market a variety of alternative technologies to reduce fuel use and lower emissions, not just HEVs and plug-ins, but also electric and hydrogen-fuel-cell vehicles.

Toyota is readying an EV for fleets in 2012 and has placed a mass-introduction date of 2015 on FCVs.