In its latest survey, fleet leasing company Godfrey Davis Contract Hire (GDCH) shows emissions fell by 5g/km in the last 12 months.
The decrease of 2.9% compares to the 1.9% reduction announced for new cars by the Society of Motor Manufacturers and Traders (SMMT) last month. It recorded the average C02 level for new cars as 174.2g/km.
But the GDCH CO2 Tracker, which measures quarterly the emissions of both new registrations for its fleet of 30,000 vehicles, shows that the average CO2 for cars joining its fleet in March was 168.1g/km.
Nigel Underdown, head of customer relationships for Bank of Scotland Vehicle Management, said: 'Our own research shows that 70% of company car drivers are influenced by CO2 emissions when selecting a car. The introduction of emissions-based company car tax has, as the Chancellor intended, helped to steer drivers into more tax efficient, more environmentally-friendly cars.'