asked Her Majesty's Government:

What carbon savings they estimate would result from (a) full compliance with current speed limits; and (b) a reduction of speed limits by 10 miles per hour. [HL7459]

We do not have estimates for the total carbon emissions from vehicles travelling in excess of 70 miles per hour for each of the past five years. As part of the review of the UK climate change programme, however, the Government have looked at the potential carbon savings that might result in the year 2010 under a wide range of different policy scenarios. These included one scenario under which no vehicles exceeded the speed limits on motorways and dual carriageways. Our estimates suggest that savings in the region of 0.5 million tonnes of carbon per annum could theoretically occur under such a scenario. In practice, however, it would be virtually impossible to enforce blanket compliance with the 70 miles per hour speed limit, and the Government have no intention of introducing such a policy. With regard to the effect of carbon emissions as a result of a reduction in speed limits, I would refer the noble Lord to my Answer of 5 July 2006 (Official Report, col. WA 43).