Author: By DAVID JOLLY

With a billion additional cars coming to the world’s roads in coming decades, reducing the carbon footprint of autos faces an uphill journey.

Skeptics, however, wonder whether the country’s program of government subsidies is cost-effective, or even an efficient way to reduce air pollutants.

The carmaker's experimental Hybrid Air has a reversible hydraulic pump that uses braking energy to compress nitrogen gas for greater fuel efficiency.