Amid the calls for drivers to slow down for safety reasons, a second, long-term benefit from more temperate travel speeds has been largely overlooked. Staying within the speed limit could significantly reduce the level of carbon dioxide emissions from motor vehicles, it has emerged.
According to a recent study by the UK Energy Research Centre, strict enforcement of a 60mph (equivalent to the 100km/h limit in Ireland) would reduce vehicle emissions of CO2 by 7 million tonnes a year, or 5.4 per cent.
David Taylor chief executive of SEI said: "During the 1970s general speed limits (in Ireland and many other countries) were reduced from 60 mph to 55 mph for that very reason, ie to reduce fuel consumption. Such a measure may only be sustainable in the short term as a response to an emergency situation.
"Measures that assist a smooth flow of traffic are likely to produce multiple benefits in terms of safety, fuel efficiency, emissions and the efficient execution of business. Buying a fuel efficient car and using it sensibly is a good place to start."
If the findings of the British report were enforced, the authors say, the savings could account for 29 per cent of the total transport sector carbon savings in Britain by 2010.
A car's fuel efficiency declines swiftly at higher speeds. A family sized petrol car emits 14 per cent more carbon dioxide per mile at 112km/h than at 100km/h.
The UK Energy Research Centre is funded by the British Government. Its study suggests using speed cameras to calculate a vehicle's average speed between two points to try and keep speeds down, rather than stand alone cameras.
The study also says that a 60mph (100km/h) limit on motorways would reduce congestion, although such a limit would be deeply unpopular with drivers.
In Ireland road transport accounted for a quarter of all carbon dioxide emissions (CO2) in the State last year.
Transport pollution is contributing to the State being one of seven EU member states which are not on target to meet their Kyoto targets on emissions blamed for causing climate change, according to a statement from the European Commission earlier this week.
The Commission was basing its estimates on projections from the European Environment Agency. Ireland's carbon emissions are expected to rise by 29 per cent by 2010, or 16 points higher than the Kyoto target agreed by the Government in 1998.
According to a report last month from Sustainable Energy Ireland (SEI), private cars are responsible for 59 per cent of fuel usage.
The authors of this report note that fuel consumption for new petrol cars on the road last year was 7.2 litres per 100km (40mpg), an increase of 1.6 per cent on average consumption in 2000.
This suggests that newer cars are becoming less fuel efficient, despite manufacturers claims to the contrary. The report says there has been no improvement in CO2 emissions in cars coming onto our roads between 2000 and 2005.
Contributing to this trend could also be the fact that car buyers are trading up to vehicles with a larger engine. The number of cars with engine sizes of 1.2 litres or less are declining. The number with engine sizes above 1.9 litres has almost doubled since 1990, according to the report.
While the number of miles driven per car is falling - according to data from NCT centres - the report notes that the number of vehicles per head of population continues to rise, with the number of two-car households rising rapidly.
Last year there were 507 cars for every 1,000 adults in the State, almost double the 312 in 1990. However, there are 718 licence holders per 1,000 adults, suggesting that there is still potential for growth. The average in EU-15 countries is 594 and the average in the UK is 555. The average for the EU25 is 558.
The report also found a 264 per cent increase in fuel consumption by road freight between 1990 and 2005, attributed in part to the high number of construction and road building trucks on the roads.
David Taylor says there should be a stronger correlation between car tax and CO2 emissions rather than simply engine size. "I think the Minister is considering this," he said.
The study found that the numbers of cars with engine sizes of 1.2 litres or less are declining while larger engines have become more popular. The number with engine sizes above 1.9 litres has almost doubled since 1990.
Vehicle manufacturers have been criticised in a recent report from the European Federation for Transport and Environment. This found that 15 out of the 20 major car brands were failing to introduce fuel efficiency improvements fast enough for Europe to meet its obligations under Kyoto.
According to the report, Renault is on target to meet a target of 140 grams of carbon dioxide per kilometre for the average new car sold in 2008. Renault is Europe's second biggest selling brand.
However, with other makers the process is less promising. Volkswagen - the biggest selling brand - has achieved less than half the improvement required. Six other manufacturers have cut emissions by less than half the rate required: Nissan, Suzuki, Mazda, Audi, Volvo and BMW.
Fiat is on course to achieve the greatest CO2 reductions across its range, followed by Citroën, Renault, Ford and Peugeot.
The European Federation for Transport and Environment noted that it was not enough for a manufacturer, such as Toyota, to have one very efficient model, selling in limited numbers. It said vehicle manufacturer must improve fuel efficiencies across their entire range.
