§ Mr. Michael McNair-Wilsonasked the Minister of Transport what is the most economic speed in terms of fuel consumption for cars and lorries; if he will list these speeds tabulated against engine size, and differentiate between vehicles using petrol and those run on diesel oil; and if he will give the research basis for his figures.
§ Mr. FowlerStudies carried out by the Transport and Road Research Laboratory, including assessment of the effects of road and traffic conditions, suggest that the most economic average speed in terms of fuel consumption is in the range of 35–45 m.p.h. for petrol engined cars and approximately 40 m.p.h. for diesel engined lorries. Differences in engine size do not in themselves seem to have a significant influence on consumption.