The nascent electric vehicle market marked an important step forward when Nissan Motor Co. announced Friday it will roll out its Leaf car Dec. 20, but zero-emission cars have to overcome many hurdles before they become widespread.

"We believe this will be the beginning of the new era for the world's automobile industry, as well as a sustainable low-carbon society," Nissan Chief Operating Officer Toshiyuki Shiga said.

Shiga emphasized that the Leaf has gotten off to a good start, with 6,000 already on order — Nissan's initial sales target for the 2010 business year.