Accredited official statistics

Notes and Definitions

Published 12 June 2025

Applies to England, Scotland and Wales

About this document

This document provides notes and definitions for the road traffic estimates published by the Department for Transport.

Road traffic statistics provide estimates of the vehicle miles travelled each year in Great Britain. We release both quarterly and annual estimates. To monitor transport activity on a timelier basis for topical issues relating to transport, daily traffic trends are published monthly.

All road traffic estimates are published through the road traffic statistics collection on the DfT statistics web page.

For more detailed information on the methodologies and data sources used to produce road traffic estimates, please review the guidance available on the road traffic statistics information page.

Definitions

Measurements of traffic

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

Vehicle mile/kilometre: One vehicle times one mile/km travelled (vehicle miles/km are calculated by multiplying the AADF by the corresponding length of road). For example, 1 vehicle travelling 1 mile a day for a year would be 365 vehicle miles. This is sometimes known as the volume of traffic.

Types of vehicle

The definitions for the vehicle types included in the traffic census are as follows:

All motor vehicles: All vehicles except pedal cycles.

Cars and taxis: Includes passenger vehicles with nine or fewer seats, three wheeled cars and four wheel-drive ‘sports utility vehicles’. Cars towing caravans or trailers are counted as one vehicle.

Motorcycles and scooters: Includes motorcycles, scooters and mopeds and all motorcycle or scooter combinations.

Buses and coaches: Includes all public service vehicles and works buses which have a gross weight greater than 3.5 tonnes.

Vans (Light Commercial Vehicles - LCVs): Includes goods vehicles not exceeding 3.5 tonnes gross vehicle weight. Includes all car-based vans and those of the next largest carrying capacity such as transit vans. Also included are ambulances, pickups and milk floats.

Lorries (Heavy Goods Vehicles - HGVs): Includes all goods vehicles over 3.5 tonnes gross vehicle weight.

Rigid heavy goods vehicles (HGVs)

• Rigid HGV with two axles: Includes all rigid heavy goods vehicles with two axles. Includes tractors (without trailers), road rollers, box vans and similar large vans. A two axle motor tractive unit without trailer is also included

• Rigid HGV with three axles: Includes all non articulated goods vehicles with three axles irrespective of the position of the axles. Excludes two axle rigid vehicles towing a single axle caravan or trailer. Three axle motor tractive units without a trailer are also included.

• Rigid HGV with four or more axles: Includes all non articulated goods vehicles with four axles, regardless of the position of the axles. Excludes two or three axle rigid vehicles towing a caravan or trailer.

Articulated heavy goods vehicles (HGVs) When a heavy goods vehicle is travelling with one or more axles raised from the road (sleeping axles) then the vehicle is classified by the number of axles on the road, and not by the total number of axles. Articulated goods vehicles with three and four axles are merged into one category, as they are not differentiated during manual traffic counts.

• Articulated HGV with three axles (or with trailer): Includes all articulated goods vehicles with three axles. The motor tractive unit will have two axles and the trailer one. Also included in this class are two axle rigid goods vehicles towing a single axle caravan or trailer.

• Articulated HGV with four axles (or with trailer): Includes all articulated vehicles with a total of four axles regardless of the position of the axles, i.e. two on the tractive unit with two on the trailer, or three on the tractive unit with one on the trailer. Also includes two axle rigid goods vehicles towing two axle close coupled or drawbar trailers.

• Articulated HGV with five axles (or with trailer): This includes all articulated vehicles with a total of five axles regardless of the position of the axles. Also includes rigid vehicles drawing close coupled or drawbar trailers where the total axle number equals five and articulated vehicles where the motor tractive unit has more than one trailer and the total axle number equals five.

• Articulated HGV with six or more axles (or with trailer): This includes all articulated vehicles with a total of six or more axles regardless of the position of the axles. Also includes rigid vehicles drawing close coupled or drawbar trailers where the total axle number equals six or more and articulated vehicles where the motor tractive unit has more than one trailer and the total axle number equals six or more.

Pedal cycles: Includes all non-motorised pedal cycles and includes electric bicycles. Estimates for pedal cycle traffic only include cycling on public highways, and on cycle paths and footpaths adjacent to them. Cycle activity elsewhere (for example on canal towpaths, byways or bridleways) is not included in road traffic statistics.

Types of road

The road definitions included in the road traffic estimates are as follows:

Road ownership/management

• Trunk roads (designated by the Trunk roads Acts 1936 and 1946): 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 Welsh Government and the Scottish Government (National Through Routes).

• Non-trunk roads: These are roads for which local authorities are highway authorities. The Secretary of State, the Scottish Government, and the Welsh Government have power to classify non-trunk roads in agreement with the local highway authority. Non-trunk roads are therefore either classified or unclassified, the former being of two types, principal and non-principal. The classified principal roads are class ‘A’ roads, except for a few local authority motorways, and are of regional and urban strategic importance. The non-principal roads are those which distribute traffic to urban and regional localities. The non-principal classified roads are sub-divided into ‘B’ and ‘C’ classes. Unclassified roads are those in the least important categories, i.e. local distributor and access roads.

• Principal roads: These are major roads which are maintained by local authorities. They are mainly ‘A’ roads, though some local authorities do have responsibility for some motorways.

• Private Roads: For the purposes of this publication, private roads are considered to be roads not maintained at public expense. For major roads, private roads (usually toll roads, tunnels and bridges) are included in the road length figures as they are accessible to the general public. For minor roads, private roads are not included in the road length figures as they are not usually accessible to the general public.

Major roads: Includes motorways and all class ‘A’ roads. These roads usually have high traffic flows and are often the main arteries to major destinations.

• Motorways (built under the enabling legislation of the Special Roads Act 1949, now consolidated in the Highways Acts of 1959 and 1980): Includes major roads of regional and urban strategic importance, 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: These can be trunk or principal roads. They are often described as the ‘main’ roads and tend to have heavy traffic flows though not as high as motorways.

Minor Roads: These are ‘B’ and ‘C’ classified roads and unclassified roads (all of which are maintained by the local authorities), as referred to above. Class III (later ‘C’) roads were created in April 1946. ‘B’ roads in urban areas can have relatively high traffic flows, but are not regarded as being as significant as ‘A’ roads, though in some cases may have similarly high flows. They are useful distributor roads often between towns or villages. ‘B’ roads in rural areas often have markedly low traffic flows compared with their ‘A’ road counterparts. ‘C’ Roads are regarded as of lesser importance than either ‘B’ or ‘A’ roads, and generally have only one carriageway of two lanes and carry less traffic. They can have low traffic flows in rural areas. Unclassified roads include residential roads both in urban and rural situations and rural lanes, the latter again normally having very low traffic flows. Most unclassified roads will have only two lanes, and in rural areas may only have one lane with “passing bays” at intervals to allow for two-way traffic flow.

Rural and urban definitions The rural and urban definitions used in road traffic estimates are based on the Office for National Statistics classification.

• Urban roads: These are major and minor roads within an urban area with a population of 10,000 or more in England and Wales, and with a population of 3,000 or more in Scotland.

• Rural roads: These are major and minor roads outside urban areas.

Notes on quarterly provisional road traffic estimates tables

These notes relate to the quarterly provisional road traffic estimates tables TRA2501 to TRA2512.

Provisional quarterly traffic estimates are based on traffic data collected continuously from a national network of around 300 Automatic Traffic Counters (ATCs). In addition to counting traffic, the ATCs record some of the physical properties of passing vehicles which are used to classify traffic by type.

Quarterly estimates are provisional until they have been constrained by the final annual estimates each year.

The background quality report for the provisional estimates outlines the process for calculating quarterly traffic estimates.

Notes on annual road traffic estimates

Annual road traffic estimates are mainly based on around 8,000 manual counts, which are combined with Automatic Traffic Counters (ATC) data and road lengths to produce overall estimates.

The background quality report for annual estimates outlines the process for calculating annual traffic estimates.

The total activity of traffic on the road network in Great Britain is measured in vehicle miles/kilometres. Different procedures are used to calculate traffic estimates for major and minor roads:

Major road traffic:

The Department produces estimates of annual average daily flow (AADF) for each link of the major road network. They are produced using 12-hour manual data counts from a large number of sites and traffic profiles derived from automatic counters.

Traffic estimates are calculated for each link of the network by multiplying the AADF by the corresponding length of road factored up by the numbers of days in the year. Therefore, a major road link of length 2 miles with an AADF of 50,000 has a traffic figure of 100,000 vehicle miles (2*50,000). This equates to 36.5 million vehicle miles a year. Because every major road link is counted, in principle, total traffic on major roads can be obtained by summing the traffic figures for every link.

Minor road traffic:

Traffic for the latest year is obtained by calculating changes in traffic flows from a sample of minor road manual counts.

Notes for annual road traffic estimates tables

Traffic volume: TRA0101 to TRA0206 Traffic estimates in vehicle miles and vehicle kilometres are presented by vehicle type, road class and region.

Traffic flow: TRA0301 to TRA0308 Tables TRA0301 to TRA0303 show annual average daily flows (vehicles per day). Average daily flow estimates for individual sections of major road are available on the Department’s website.

Tables TRA0305 to TRA0308 show distribution of traffic flows by month, day of the week and time of day. These data are collected by Automatic Traffic Counters and have been scaled to show the average flow across each time period.

Road traffic on England’s road network: TRA4101 to TRA4216 Between 1999 and 2012, a detrunking programme ran which resulted in stretches of road, in particular ‘A’ roads, that were previously part of the National Highways (NH) managed roads becoming the responsibility of local authorities. Over this period, the length of the road managed by NH reduced by 12.6%. Therefore, in tables TRA41xx, trends between 1999 and 2012 will mostly show the effect of the detrunking programme. Tables TRA42xx have been created to enable a consistent analysis of the trends from 2000. In tables TRA42xx figures for 2000 to 2012 are calculated based on road management responsibility as it was on 1 April 2012. As a result, roads that were detrunked during this period are included in the figures for local authority (LA) managed roads for the full time series regardless of when the road moved from being National Highways (NH) managed to the LA managed.

Road traffic for local authorities: TRA8901 to TRA8906 Traffic volume estimates (vehicles miles/kilometers) are presented by road class at a regional and local authority level. Traffic flow estimates are also presented by road class at a regional level.

Estimates of road traffic at local authority level are less robust than the regional and national totals and are not classed as Accredited Official Statistics.

Foreign registered vehicles in traffic: TRA3201 to TRA3203: These tables show the proportion of vehicles in traffic which are registered outside the UK, by vehicle type, road type and region.

During June, every other year, a roadside survey is carried out collecting information about vehicles travelling on the road. Vehicles with registration marks originating outside the United Kingdom have been identified and this information has been used to produce estimates of the rate of foreign registered vehicles on Britain’s roads.

As the sample size is relatively small (there were over 7,000 observations of foreign registered vehicles out of 1.1 million total observations) these figures are not designated as Accredited Official Statistics and should be treated with caution. Particular attention should be paid to the confidence interval associated with each statistic and in some cases statistics have not been produced as the sample size is too small.