What are Ireland’s cleanest cars? That was the question that came into Motors from a reader and as usual, we decided to do our best to find out.

These are Ireland’s cleanest cars, based on C02 emissions and it serves to illustrate just how far cars have come in the last few years. When the changes came to the road tax and VRT laws in July 2008, there were only a handful of cars that occupied Band A and now, within a short space of time this category has grown.

Toyota Auris Hybrid: forthcoming model will have emissions of 89g/km

The average new car sold in Ireland this year has emissions of 135g/km. Over the same period last year the average was 150.6g/km. On average, new cars purchased in 2007 emitted 3.6 tonnes of CO2 per annum and the ”average” car in 2007 had a rating of 164 g CO2/km and would  be classified as ’D’ under the current labelling scheme  attracting annual road tax of €430.

This dramatic drop in average emissions since 2007 from 164g/km to 135g/km this year can in part be attributed to the advances in new technology, but it can also be largely attributed to taxes. Back in 2007, if car’s had been classified by their CO2 emissions, the most popular Band was Band D, with 45,596 (24.8 per cent) cars having emissions of between 156-170g/km.

This was closely followed by Band C, from 141-155g/km with 43,160 units (23,17 per cent). Perhaps a sign of the times was that the third most popular Band was Band E, with 40,382 units (21.68%) of the market. There were just 903 or 0.48 per cent of new cars sold with emissions of 120g/km or less, mainly because they didn’t exist.

Back in 2007 petrol powered cars made up 70.99 per cent of the market and diesel 27.99 per cent.

Look at 2010 and the shift towards lower emissions is also reflected in the tax bands, where 75 per cent of new cars now fall into band A or B. 44.78 percent of these are Band B cars, with emissions of 121-140g/km and Band A now makes up 33.48 per cent of the new car market. This year, so far, 63.87 per cent of new cars sold are powered by diesel with just 32.23 per cent powered by petrol engines. Band E, the third most popular segment in 2007 now makes up just 2.43 per cent of new car sales.

But would Irish buyers have made the switch to these cleaner cars all on their own if the penalties for driving higher emission vehicles hadn’t been so punitive? I seriously doubt it. The executive SUV segment, for example, fell 92 per cent because of the new system.

It hasn’t been all bad for the executive buyer however, as advances from the German car firm’s in particular have meant that Ireland’s CO2 emission regulations have seen tailor made for them. The BMW 520d is a prime example. Here is a car that used to cost around €55,000 for a half decent one and now you can have the new model, which has emissions of less than 137g/km for less than €42,000 because you pay less VRT on it and significantly lower road tax. The top-selling car in August this year was the BMW 520d. The same is true for the Mercedes-Benz E-Class, which is now a major beneficiary of the new tax system, costing close to €20,000 less than it did three years ago.

BMW 520d: Top selling model in August

However, if you look at the list of the cleanest cars for this year, you will note that 13 of them have emissions of less than 100g/km and currently there is no extra incentive to buy these, unlike many other countries in Europe. Perhaps now it is time to revise the current system to reflect the work that is being done by manufacturers to reduce emissions even further.