Question to the Department for Transport:

To ask Her Majesty's Government what evidence they use to inform policy about vehicle (1) speed limits, and (2) emissions; and what assessment they have made of the emissions levels of (a) petrol, and (b) diesel, vehicles between 1,000–3,000cc travelling at a constant speed of 20mph in (i) first gear, (ii) second gear, (iii) third gear, (iv) fourth gear, (v) fifth gear, and (vi) sixth gear.

The aim of speed management is to deliver a balance between safety objectives for all road users and mobility objectives, to ensure efficient travel, as well as environmental and community outcomes. The Department has published guidance designed to make sure that speed limits are appropriately and consistently set while allowing for flexibility to deal with local needs and conditions.

The regulatory emissions tests for type approval of new vehicles are conducted under dynamic rather than constant speeds in order to be more representative of real-world use. The Department does not have specific results for the situations outlined. Transport emission factors are used within the National Atmospheric Emissions Inventory to provide information on the emissions of vehicle fleets based upon factors such as their average speed, fuel type and engine capacity. These are also used within the Emissions Factor Toolkit, published by DEFRA, to assist local authorities carrying out assessment of local air quality.