The national speed limit of 70 miles per hour on dual carriageways and motorways reflects a practical balance between economic, environmental and safety objectives.
As part of a review of the UK Climate Change Programme, the Government have looked at the potential carbon savings that might result in 2010 under a range of different policy scenarios. One of these scenarios is a reduction of the speed limit on motorways and dual carriageways from 70 miles per hour to 60 miles per hour. The results of the analysis suggest that, if the new limit was strictly enforced, there could be carbon savings of around 0.84 million tonnes of carbon. However, such strict enforcement would not be easy to achieve in practice and could have significant implications and costs in its own right. Indeed, the analysis suggests that such a policy would not be cost-effective, with the benefits likely to be significantly outweighed by the costs.