AMERICAN group Environmental Defense recently cited Toyota and BMW as the only carmakers in the United States to have cut average per-vehicle carbon dioxide emissions between 1990 and 2005.

Toyota's variable-valve timing engine, used in the best-selling Corolla, contributed much to its results. BMW improved average fuel economy by 14 per cent and reduced CO2 emission rate by 12.3 per cent in the 15-year period - more than any other major automaker.