To ask the Secretary of State for Transport pursuant to the answer of 4 February 2008, Official Report, column 792W, on transport: carbon emissions, if she will estimate the percentage of carbon dioxide emission reductions by 2020 likely to come from (a) policy measures and (b) technological developments independent of Government policy. (186836)

It is not possible to separate the impacts of policy measures from technological developments that have occurred independently of Government policy. This is because many policy measures to reduce CO₂ (for example, graduated VED or standards for new car CO₂) will affect both the production and consumption of fuels and vehicles, and these processes interact.

However, in our modelling of the impacts of policies to improve new car fuel efficiency (including the EU voluntary agreements, graduated vehicle excise duty, company car tax, vehicle labelling) we assume that there would have been no improvements in new car fuel efficiency in the absence of these policy measures. This is because analysis of historic trends suggests that any ‘natural’ improvement in fuel efficiency would have been balanced by worsening fuel efficiency from a trend towards heavier vehicles.