According to data released by the UK's Society of Motor Manufacturers and Traders, new cars registered there during 2011 were, on average, 18% more efficient than the average car on the road. The society has released its 11th annual New Car CO2 report that analyses emissions data from all new cars registered in the UK. The data revealed an improving fuel efficiency and falling emission trend – average CO2 emissions of 138g/km in 2011 were lower by 4.2%, compared with 2010 data, and is down by more than 23% since reporting began in 2000. According to the 2011 report, more than 65 000 vehicles were exempt from road tax as cars with 100g/km and less CO2 emissions ratings almost doubling their market share to 3.4%. THE BIGGEST LOSERSReductions in average emissions were made across all vehicle segments versus 2010. The biggest reductions were seen in the Executive and Specialist Sports segments (down 9.5 and 7%, respectively) while, compared with 2000 data, Executive (-34.9%) and Mini (29.9%) registered the biggest improvements. Achieving record market shares, diesel and alternative fuel vehicles (AFV) continued their rise in popularity, taking 50.6% and 1.3% of the 2011 market respectively. Petrol-electric hybrids accounted for 92% of all AFV volumes in 2011 with an average CO2 output of 104g/km, 25% below the UK average.Despite these advances, the SMMT has urged the UK government to be consistent about its taxation and expand incentives that encourage consumers to move towards vehicles using more fuel-efficient technologies. Read the full SMMT New Car CO2 Report.