Estimating road traffic emissions is an increasingly important part of a local authority's duties. For example, the local air quality management process requires an assessment of emissions from traffic and Local Transport Plans must make an assessment of the impacts of proposed transport schemes on the environment. Traffic composition is an important factor in estimating emissions, but whilst details of typical vehicle-mixes are available for some roads, for others national statistics are the only realistic alternative. The national 'average' may not adequately describe the local situation for the purpose of accurately estimating emissions. This report describes a study to investigate and provide a classification of traffic composition, by geographical area and location type, that could be used in local air quality assessments. Relationships have been derived using a number of sources to describe how average speed, engine size, fuel type, trip length, vehicle age profile and HGV weight distribution vary with road type (motorway to rural B&C roads), area type (London inner to rural) and year (1996 to 2010). These relationships are then provided as a series of tables to be used with vehicle flows that are classified according to the proportion of cars, LGVs, HGVs and buses and coaches. (A)

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