§ Ms. WalleyTo ask the Secretary of State for Transport (1) if he has assessed the possible effect of more stringent enforcement of speed limits on emissions of carbon dioxide and oxides of nitrogen from road traffic;
(2) what would be the effect on emissions of carbon dioxide and oxides of nitrogen from road traffic if speed limits on motorways were (a) increased to 80 mph and (b) reduced to 50 mph.
§ Mr. Chope[holding answer 28 January 1991]: The precise effect of a change in speed limits or enforcement would depend on the way in which average driving speeds were affected. The available evidence suggests that, typically, reducing average speed from 70 to 50 mph would reduce a car's CO2 emissions by about 20 per cent. and NOx emissions by about 25 per cent.
The rate of CO2 emissions would increase proportionately more rapidly from 70 to 80 mph and NOx emissions would also rise.