This despite previously arguing that with a car like the Leaf, more efficiency is the goal, even if it means less soul.

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The researchers, from the University of Oregon and the Oregon State University, supports previous research showing the survival of a leaf-cutter colony depends on the efficiency of its workers.

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Due to efficiency improvements, the 2013 Nissan LEAF is expected to offer improved range, with testing on the EPA test cycle to be announced closer the vehicle's on-sale date.

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The Ford Focus Electric has received a 110 MPG equivalent fuel efficiency rating in the city and a combined fuel efficiency of 105 MPGe, 6 MPGe more than the all-electric Nissan Leaf.

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"The Nissan LEAF has an advantage in that braking force is used to re-power the battery, thereby improving its energy efficiency, " said Castignetti.

ENGADGET: Nissan starts US production of 2013 Leaf, vows faster charging and a lower entry price