DfT > AADFs > Data Definitions

Data Definitions

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Introduction

There are 3 types of definition as listed below:

·         Road categories: Provides the definitions for the different road types used by the Department for Transport.

·         Data table descriptions: Provides the data item name, the label name and a data description for the data sets that can be downloaded from this web site. The data includes network and annual average daily traffic flows.

·         Look-up table descriptions: Shows the data item name, heading label and data description for the look-up tables for the local Highway authority, the regions and the road categories.

Look-up tables

·         Look-up table values: Lists the local Highway authorities, the regions and the road categories in the look-up tables.

Road Classes

·         Major roads: Include motorways and A roads. These roads usually have high traffic flows and are often the main arteries to major destinations.

·         Motorways: Major roads often used for long distance travel. They are usually three or more lanes in each direction and generally have the maximum speed limit of 70mph.

·         A Roads: Can be trunk or principal roads. These are often described as ‘main’ roads and tend to have heavy traffic flows though not as high as motorways.

·         Trunk roads: Most motorways and many of the long distance rural A roads are trunk roads. The responsibility for their maintenance lies with the Secretary of State and they are managed by the Highways Agency in England, the National Assembly of Wales in Wales and the Scottish Executive in Scotland (National Through Routes).

·         Principal roads: These are major roads maintained by local authorities. They are mainly A roads (though the local authorities do have responsibility for some motorways) and tend to be in urban areas.

·         Minor roads: These are B roads, C roads and unclassified roads and are all maintained by the local authorities. Data for minor roads are unavailable.

·         Urban roads: Major and minor roads within an urban area, i.e. an area with a population of 10,000 or more. The urban areas used are based on 2001 Census data. The definition is based on the 2001 'urban settlement' and is available in Urban and rural area definitions: a user guide which can be found on the DCLG web site at:

http://www.communities.gov.uk/planningandbuilding/planningbuilding/planningstatistics/urbanrural/

·         Rural roads: All other roads, i.e. those outside urban areas (urban areas having a population of 10,000 or more - see above).

Measures of traffic

·         Count Point (CP): Traffic estimates are calculated for each link of Great Britain's major road network, with links' start and end points defined as where the link joins a major road junction. Each link has a uniquely referenced Count Point (CP), where the traffic is usually counted by enumerators. Enumerators are not employed where (a) the CP is dependent upon another CP, i.e. the traffic estimate is calculated for each side of a Local Authority boundary, or (b) the traffic estimate is derived from neighbouring CPs' traffic estimates. Unlike the major road network (where every link has a CP), there are CPs on a sample only of minor roads.

·         Annual Average Daily Flow (AADF) - measured in number of vehicles: The average over a full year of the number of vehicles passing a point in the road network each day.

·         Traffic - measured in vehicle kilometres: One vehicle times one kilometre travelled times the numbers of days in the year (vehicle kilometres are calculated by multiplying the AADF by the corresponding length of road factored up by the numbers of days in the year). For example, 1 vehicle travelling 1 kilometre a day for a year would be 365 vehicle kilometres. This is sometimes known as the volume of traffic. The output statistics are presented as 1,000s of vehicle kilometres. For instance, a CP with a traffic volume of 20,000 vehicle kilometres in one year will be presented as 20.0.

Data Table Descriptions

Major Roads Network

Annual Average Daily Flows (AADF) and Traffic

Footnote:
1. Goods vehicles over 3,500 kgs gross vehicle weight. Includes tractors (without trailers), road rollers, box vans and similar large vans. A two axle motor tractive unit without trailer is also included.

Look-up table descriptions

 LACode - Local Highway Authority   

 Region - Government Office Region   

 RCat - Road category   

Look-up table values

LACode - Local Highway Authority