While the car is on the move, the electric drive itself contributes to a favourable energy balance through recuperation, by converting kinetic energy into electric current in deceleration mode and during braking and feeding this energy into the battery.
But the US appears to be growing as an obstacle, with campaigners acknowledging privately that the balance of power in Congress is likely to become even less favourable to carbon-cutting legislation after the next round of elections in 2012.