Consumers are purchasing significantly more energy efficient cars, as a result of the Government's changes to vehicle registration tax.
Sustainable Energy Ireland said private car sales, in the most efficient emission bands, jumped from 43% to 73% after the introduction of new VRT rates.
SEI's Dr Brian Motherway said it was notable that this change has not entailed a move towards smaller engine sizes, but a marked shift towards diesel-fuelled cars.
Between the first and second half of 2008, diesel cars have doubled their share of sales.
Even with lower vehicle sales in the first half of 2009, energy efficient cars comprised 78% of new cars purchased and diesel cars comprised 56% of new cars purchased.
Average CO2 emissions of new cars purchased in the 12 months between July 2008 and 2009 have fallen by 12%.
In its latest Energy in Transport report, SEI says the recession has affected all transport patterns and energy use, with freight transport showing a 6.7% decrease after an average growth of over 8% for many years.
Ireland's total vehicle fleet continues to grow with almost 2.5 million vehicles in the state in 2008, a 2.3% increase on 2007.
Dr Motherway said: 'Transport is a huge fuel user, accounting for more than one third of Ireland's total primary energy demand.'
