Accredited official statistics

Background Quality Report

Published 12 June 2025

Applies to England, Scotland and Wales

Introduction

This background quality report relates to the annual release: Road traffic estimates in Great Britain. The purpose of this document is to provide users of these statistics with information about the methodology adopted and quality of the outputs, measured against different dimensions of statistical quality. It also provides information about how the department has responded to previous user feedback, as well as planned developments.

As a result, this document helps to demonstrate how the department complies with the Code of Practice for Statistics.

A. Background to the statistics

1. Statistical presentation

1.1 Data description

The publication Road Traffic Estimates in Great Britain presents annual estimates of the volume of traffic on Great Britain’s roads. These estimates are split by geography, by road type, by road management status, and by vehicle type.

Annual statistics are mostly presented in units of vehicle miles, which combines the number of vehicles on the road and how far they drive. Annual traffic statistics are compiled using data from around 8,000 roadside 12-hour manual counts, continuous data from automatic traffic counters, and data on road lengths.

Traffic estimates are also produced for annual average daily traffic flow (AADF), which are measured in numbers of vehicles. In addition, the publication contains figures indicating the relative traffic volumes across the months of the year, days of the week, and hours of the day.

Alongside the annual publication, a supplementary website provides the underlying data collected to produce the summary estimates, roadtraffic.dft.gov.uk.

1.2 Classification system

Annual road traffic estimates are published split by vehicle type, road type, road management, and geography. Short descriptions are given below. Full details of the definitions used are in the Notes and Definitions document.

1.2.1 Vehicle Types

Vehicle categories are summarised in the annual road traffic estimates publication into the following groups:

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.

Vans (Light Commercial Vehicles - LCVs) - 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.

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.

Pedal cycles - Includes all non-motorised pedal cycles and includes electric bicycles.

Roads in Great Britain

Diagram 1: The management of publicly maintained roads in Great Britain

Diagram 1 shows how the publicly maintained roads in Great Britain are managed. By length, most roads in Great Britain are managed locally (by a local highway authority or Transport for London). These are principal roads and they include all minor roads (‘B’, ‘C’ and ‘U’ roads), and some major roads (principal ‘A’ roads and principal motorways). The rest of the major road network (trunk motorways and trunk ‘A’ roads) is managed centrally by National Highways (formerly Highways England) in England, the Welsh Government in Wales, and Transport Scotland in Scotland. The trunk road network in England makes up the Strategic Road Network (SRN). Motorways, ‘A’, ‘B’ and ‘C’ roads are classified roads, and ‘U’ roads are unclassified. ‘U’ roads are made up of roads that have a variety of uses but they are typically residential streets or rural lanes.

1.2.2. Road Types

The annual road traffic estimates publication summarises traffic on roads using the following categories:

Motorways - major roads of regional and urban strategic importance, often used for long distance travel.

‘A’ roads - often described as the ‘main’ roads and tend to have heavy traffic flows though generally not as high as motorways.

Minor roads - ‘B’ and ‘C’ classified roads and unclassified roads.

Urban roads - these are roads that sit within a built-up area, with a residential population of more than 10,000 in England and Wales or more than 3,000 in Scotland.

Rural roads - these are roads that sit outside urban areas.

1.2.3. Road Management

The annual road traffic estimates publication summarises traffic by road management using the following categories:

Trunk roads - includes some motorways and ‘A’ roads. Roads managed by centrally by National Highways in England, the Welsh Government in Wales, and Transport Scotland in Scotland.

Principal roads - includes some motorways and ‘A’ roads, and all minor roads. Roads managed by local highways authorities.

1.2.4. Geography

The annual road traffic estimates publication summarises traffic by the following different geographies:

• Country - England, Scotland, Wales

• Region - the 11 regions of Great Britain

• Local highway authorities – county and unitary authorities, and London boroughs

1.3. Statistical concepts and definitions

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: The number of miles travelled by vehicles over a year on a given stretch of road. Vehicle miles or kms are calculated by multiplying the AADF by the corresponding length of road and the number of days in the year - typically 365. For example, 1 vehicle travelling 1 mile a day for a year would be 365 vehicle miles.

1.4. Statistical unit

The statistical units used in the publication are:

• vehicle miles (and vehicle kilometres)
• number of vehicles, on an average day of the year.

1.5. Statistical population

The statistical population is road traffic estimates on roads in Great Britain.

1.6. Reference area

Estimates of road traffic at different geographical levels are presented. Estimates are published for each country in Great Britain, for each region, and for each local highway authority.

Estimates are also split by whether an area is defined as ‘urban’ or ‘rural’ (as defined by the Office for National Statistics’ urban/rural classification).

1.7. Time coverage

The publication contains figures for Great Britain by vehicle type and road type back to 1949. All other splits of the data for Great Britain cover the period from 1993. Estimates for England are available for the year 2000 onwards. The time series for temporal traffic distributions starts from 2006.

2. Statistical processing and methodology

2.1. Source data and frequency

There are five main data sources for these statistics:

DfT Roadside Surveys (manually enumerated counts): Annual traffic estimates are mainly based on the 8,000 roadside counts which are conducted each year. These take place on weekdays between March and November each year, outside of public and school holidays.

DfT Automatic Traffic Counters (ATCs): Traffic flow data is collected continuously (24 hours a day, 365 days a year) from the department’s national network of around 300 ATCs. In addition to counting traffic in each direction, the ATCs record some physical properties of passing vehicles which are used to classify traffic by vehicle type. ATCs operate across a range of road types and geographical regions; the data they collect is used to estimate changes in traffic and seasonal variation.

External ATC data: The DfT’s road traffic statistics also make use of automatic traffic counter data that is collected and maintained by other organisations. These are:

• National Highways (NH): operate over 10,000 automatic traffic counters on some of the motorways and ‘A’ roads in England.

• Transport Scotland: operate over 1,500 automatic traffic counters on some of the motorways and ‘A’ roads in Scotland.

• Transport for London (TfL): operate over 300 automatic traffic counters on roads in London.

The data from these organisations are analysed by DfT after the end of each calendar year.

Road length data: Road lengths are taken from the DfT’s road length statistics, which are published annually. The road length statistics are based on information from a range of sources, including Ordnance Survey and local authorities.

For information about the calculation of major and minor road length statistics, see the guidance on the GOV.UK road length statistics web pages.

Road network data: For the motorway and ‘A’ road network in Great Britain, a simplified snapshot version of the road network is produced as at April each year – the Major Roads Database (MRDB). It is updated using data from the Ordnance Survey and the shapefile is published here.

2.2. Data collection and validation

2.2.1. DfT Roadside Surveys (manually enumerated counts)

Around 8,000 roadside counts which are conducted each year, on weekdays between March and October each year, outside of public holidays and school holidays, due to weather and light considerations at the count locations. They are undertaken over a 12-hour period (7am to 7pm). Trained enumerators either observe and count traffic from the side of the road, or set up cameras to do so and count the traffic at a later time. The locations of the counts are given a unique reference number called a count point number (CP).

Roadside counts on major roads: Every junction-to-junction link of the motorway and ‘A’ road network in Great Britain is assigned a CP number. However, it is not possible to count every single location every year; therefore, the sections of road are surveyed on either an annual basis or on a cycle of every 2 years, every 4 years or every 8 years (and in Scotland and Wales, every 12 years). The frequency is based on the traffic level. This means not every link in the major road network has a 12-hour count in each year.

Roadside counts on minor roads: Due to the vast number of minor roads in Great Britain it is not possible to count them all, instead a representative sample of minor road sites are counted each year.

The data collected are collated each month and provided to the department. The data are validated by comparing data points against average values and against previous data collected from the same location.

2.2.2. DfT Automatic Traffic Counters (ATCs)

Traffic flow data is collected continuously from the department’s network of around 300 ATCs. The locations are a stratified panel sample, and provide sufficient observations so that in-year traffic variations can be estimated by road type and vehicle type.

The automatic traffic counters are permanent installations embedded in the road surface, which combine Inductive Loops with Piezoelectric Sensors in a ‘Loop – Piezo Sensors – Loop’ array, and record information about vehicles passing over them, including vehicle length and wheelbase, to classify vehicles.

The data are validated using a combination of automated and manual processes to check the data, by using error codes returned from the ATC and by comparing data with historic values. Where necessary, invalid data is replaced with imputed data. There are two main reasons why ATC data is imputed:

• because the ATC is faulty and producing no data or incorrect data that needs to be imputed

• the ATC is functioning correctly but because of road works, or an event, there are extreme traffic levels on the road being sampled

The ATC data is a sample, which is being used to represent all roads in Great Britain. Therefore, events which cause anomalous traffic data are discarded and replaced with imputed data to prevent over-inflating the effect of a one-off incident at one location on total traffic estimates. Validation tests are carried out for each vehicle type independently in order to reduce the amount of imputation necessary.

2.3. Methodology: data compilation and adjustment

Once the raw count data has been collected and validated, it is used to produce AADF estimates. There are then different methodologies applied to produce traffic estimates for major roads and for minor roads.

2.3.1. AADF calculations

Major road AADFs are produced by using one of five methods – counted, grown, ATC, dependent, and derived. Minor road AADFs are mostly calculated using the counted method, with a small number calculated using the ‘grown’ method.

Diagram 2: Expansion factor and growth factor strata for the road network

Diagram 2 shows the expansion factor strata and growth factor strata used for the AADF calculations.

Counted AADFs: For major and minor road locations that have had a roadside count in the given year, the AADF is produced by multiplying the 12-hour count by the relevant expansion factor depending on vehicle type, count date and expansion factor strata.

Expansion Factors DfT ATC data is used to create expansion factors, for each day of the year, for each expansion factor strata and by vehicle type. Expansion factors for a given day are calculated by dividing the annual average daily vehicle count by the 12-hour daytime count on the given day. The average of these values is then calculated from all DfT ATCs in the given stratum.

Grown AADFs: For major roads, and a small number of minor road locations, a grown AADF is produced by applying the relevant growth factor to the previous year’s AADF, depending on vehicle type and growth factor strata.

Growth Factors DfT ATC data is used to create growth factors, for each of growth factor strata and for each vehicle type. Growth factors are calculated from the change between the reference year and the previous year.

Dependent AADFs: some major road locations are defined as dependent. A dependent AADF will have the same AADF value as the adjacent road link. This happens where the road to which they are associated crosses through a local authority boundary, then the link is simply broken into two parts and the AADF is equal for each section. Therefore, dependent AADFs are calculated after all other AADFs to ensure all data is available.

Derived AADFs: If a major road is very small (less than 300m) or is considered too dangerous to count, surrounding roads have been studied and a formula created to calculate the AADF by using the AADFs of the other links.

ATC AADFs: Some major roads have automatic traffic counters on them managed by other organisations. Those managed by National Highways, Transport Scotland and Transport for London, supply DfT with the ATC data for all motor vehicles. From this, the ‘all motor vehicle’ AADF is calculated for these roads by dividing the total count by the number of days of available data.

2.3.2. Major roads:

At this stage AADFs have been calculated for every link of road in the major road network. Traffic volume is measured in vehicle miles, where one vehicle mile is equal to one vehicle travelling one mile.

To convert the AADFs into traffic volume, each AADF is multiplied with its associated link length; then it is multiplied by the number of days in the year to get an annual total.

Traffic_CP = AADF_CP × Length_link × 365 (or 366)

As traffic volume figures are calculated for every link of the major road network, these figures can then be summed to create total major traffic volume figures for Great Britain, regions and local authorities.

Total traffic = Σ Traffic_CP

2.3.3 Minor roads

Minor road traffic estimates are produced at the local authority level although some elements of the calculation use data at high geographical levels (as set out below).

At this stage AADFs have been calculated for the panel sample of locations on the minor road network (roughly 4,000 locations). From this, for each vehicle type the average AADF is calculated. For cars, vans and HGVs, this average is calculated for each region and road type, but for the smaller vehicle types the average is calculated at a more aggregate level. The change in the average AADFs between the latest two years is then calculated.

Separately, using the road length statistics for the latest two years, the change in the local authority road length, for each road type, is calculated.

The two figures, for traffic change and road length change, are then applied to the previous year’s minor roads estimates to calculate the latest year’s estimates.

Example:

The latest year’s traffic estimate for cars on rural roads in a given region is calculated using the following formula:

Cars on rural roads_y = Cars on rural roads_y-1 x Change_traffic x Change_length

Where:

• y = latest year

• y-1 = previous year

• Change_traffic = the traffic change for cars on rural roads in the relevant region between y-1 and y

• Change_length = the change in rural road length in the relevant local authorities in the relevant region between y-1 and y

Minor roads benchmark Once a decade a benchmarking exercise is undertaken to rebaseline the traffic estimates for minor roads in Great Britain. Annual traffic estimates on minor roads are based on traffic counts at a fixed sample of locations. Although retaining a fixed sample ensures a more precise measure of traffic growth between consecutive years, it also means that any errors in the sample will accumulate over time. In order to correct for any sampling errors, a larger benchmark sample is taken every decade, this allows for the recalibration of the traffic estimates on minor roads. The aim of the benchmarking exercise is to reduce the error incurred by having a fixed sample and to give a more accurate estimate of traffic on minor roads. The larger benchmark sample is also used to select roughly 4,000 locations to form the annual minor road sample for the following decade.

More information about minor roads benchmarking can be found in the Minor road traffic estimate review reports.

3. Quality management

3.1. Quality assurance

The quality assurance frameworks for road traffic estimates are:

• the Code of Practice for Statistics

• the assessment checks by the Office for Statistics Regulation (see next section)

• the DfT standards for official statistics, including the statement on statistical quality

3.2. Quality assessment

These official statistics were independently reviewed by the Office for Statistics Regulation in February 2013. They comply with the standards of trustworthiness, quality and value in the Code of Practice for Statistics and are labelled ‘accredited official statistics’. The assessment report and confirmation letter have been published.

The annual traffic estimates publication also includes ‘official statistics’. These are the data tables presenting local authority level estimates of traffic (tables TRA8901-TRA8907), and the data tables presenting temporal distributions of traffic (tables TRA0305-TRA0308). They comply with the standards of trustworthiness, quality, and value in the Code of Practice for Statistics.

The work that the Road Traffic Statistics team have undertaken to develop improvements to the production of traffic estimates are published on road traffic statistics information page.

Recent examples:

• daily road traffic trends, which were developed during 2020 and continue to be published

• minor roads traffic estimate review, which was published in 2022

B. Quality assessment of the statistics

4. Relevance

Relevance is the degree to which a statistical product meets user needs in terms of content and coverage.

4.1. User needs

Users of our statistics include:

National Atmospheric Emissions Inventory (NAEI) Road traffic statistics are used to produce the National Atmospheric Emissions Inventory (NAEI), a legal requirement for the UN Framework Convention on Climate Change.

Transport Modelling The Department for Transport’s National Transport Model uses most traffic and speeds outputs to make forecasts and to inform policy decisions on a broad range of issues.

Local transport planning Local Authorities (including Transport for London) and devolved governments use the data for transport planning, road engineering and policy monitoring at a regional or local level.

Road collisions and safety statistics Road collisions and safety statistics use annual and quarterly traffic estimates to produce road safety and casualty rates, as used for the monitoring of road safety policies.

Ministry of Housing, Communities and Local Government This department uses traffic data on major roads to contribute towards the funding settlement for local authorities.

Public Users The DfT receives over 200,000 visits annually to the traffic counts website and its underlying datasets, which provides street-level traffic data for every junction-to-junction link on the ‘A’ road and motorway network in Great Britain.

4.2. User satisfaction and completeness

It is considered that, on the whole, the range of statistical outputs meet most needs for data from both official and non-official users of data.

This assessment is based on user engagement, including direct feedback about from people and organisations involved in road policy, monitoring and delivery in Great Britain (for example road policy and analytical teams within DfT and the devolved administrations, local authorities, researchers). Website analytics are also used to assess the level of interest in different outputs.

In addition to the annual publication, DfT provides the traffic counts website, containing the underlying datasets. This allows users to access data that are not covered by the published statistics (for example traffic on a particular stretch of road.

5. Accuracy and reliability

Accuracy refers to how close the estimated value in the output is to the true result. The concept of statistical accuracy can be broken down into sampling and non-sampling error. Non-sampling error includes areas such as coverage error, non-response error, measurement error and processing error.

5.1. Overall accuracy

The annual road traffic estimates are produced using well-established methodologies that have been in use for several decades. This approach produces robust estimates on traffic levels in Great Britain by vehicle type and by road type.

Whilst road traffic data is accurate at a high level of aggregation, it should be noted that local authority splits of the data and temporal distributions are not as robust and, therefore, these datasets are labelled as official statistics to reflect this. Further information is provided in the rest of this section.

5.2. Sampling error

Due to the multisource process it is difficult to assess the sampling error for the annual traffic estimates. In addition, as set out in the Statistical processing and methodology section, there are different approaches for major and minor roads.

For major roads, the census-based approach means that there is complete geographic coverage of all motorways and ‘A’ roads in Great Britain and so there is, by definition, no sampling error. As not all major roads are counted every year, major road traffic estimates are subject to statistical uncertainty, which will be lowest immediately following an observed traffic count, and greatest immediately before the next count, as error accumulates over time. The impact of this on the aggregate estimates is reduced by the use of DfT ATC data to produce expansion factors and growth factors. Furthermore, higher flow roads, which have a larger impact on our published estimates will undergo a roadside count more frequently.

For minor roads, there is potential for sampling error in the annual panel sample approach. The change estimates from the fixed annual sample may drift over time and the sample may vary and become less representative of the changing minor road network. To account for any error incurred in the fixed sample, the sample is revised through the minor roads benchmarking exercise every decade. The revised sample for each benchmark consists of around 10,000 minor road locations, with around 4,000 of these locations forming the annual minor road sample for the following decade. For more information about the latest benchmarking exercise please see the minor roads traffic estimate review

5.3. Non-sampling error

There are two potential types of non-sampling errors in the road traffic estimation - measurement error and processing error.

The DfT ATCs, used to produce the expansion and growth factors, classify vehicle types based on characteristics such as axle-spacing and vehicle length. This creates the possibility for measurement errors from the misclassification of vehicles with atypical characteristics. The ATC classification algorithms and the ATC validation checks are continually developed to ensure that vehicle classification is as accurate as possible.

Given the size of the datasets used to produce road traffic estimates, it is inevitable that there will be some processing errors. The breadth and depth of the data validation work, as outlined above, aims to mitigate these, although the final datasets will still contain some errors and missing data. On the whole, these are not considered to impact on the patterns and trends shown.

5.4. Data revision

5.4.1. Data revision – policy

Road traffic estimates for Great Britain are usually revised once a decade following the planned minor roads benchmarking exercise. Further information about this regular, pre-announced benchmark revision can be found in the minor roads section.

The DfT statement on revision policy sets out how revisions are handled for all statistical outputs, including the annual road traffic estimates. Minor revisions will take place at the next scheduled publication of the series. Substantial revisions, where the revision changes the story or overall trend, will have actions determined by the Head of Profession for Statistics.

5.4.2. Data revision – practice

Planned revision

In 2021 the road traffic statistics team announced it was conducting a review of the historic minor road traffic estimates, and provided details of the scope of the review and that it would be completed alongside the publication of the 2022 road traffic estimates for Great Britain.

The aim of the review was to identify areas that would improve robustness and consistency of the historic time series. The overall approach to producing annual minor road traffic estimates was not changed as a result of the review. However, the methodology used to calculate minor road traffic estimates from the minor road benchmarking exercises in 2009 and 2019 was revised following investigations into areas for improvements. One of the key areas from the review was to use GPS data to stratify the benchmark sample into ‘low’ and ‘high’ traffic flow locations. As a result, annual minor road traffic estimates were revised from 2000 to 2020 in the ‘Road traffic estimates in Great Britain: 2021’ publication.

Full details of this review were published on the road traffic statistics information page.

6. Timeliness and punctuality

Timeliness describes the time between the date of publication and the date to which the data refers, and punctuality describes the time between the actual publication and the planned publication of a statistic.

6.1 Timeliness

Road traffic estimates in Great Britain are published once a year, usually in May or June (a gap of around 6 months between the final data period and publication).

Improvements to the efficiency of the process for producing and quality assuring the data could allow this to be brought forward in future years.

6.2 Punctuality

Punctuality is usually a minor issue as all outputs adhere to the Code of Practice for Statistics by pre-announcing the date of publication on the gov.uk website. In recent years, there have been some cases where methodological reviews and/or improvement projects have resulted in statistics being published later than the usual timetable. For example, annual estimates for 2021 were pushed back from June to September to allow time to complete the minor road traffic estimate review of historic estimates. In this case, changes to the planned publication date were announced well in advance, and there have been no occasions where pre-announced statistics have not been published as planned.

7. Coherence and comparability

This covers the ways statistics can be combined and used reliably. Coherence refers to the extent to which statistics produced by different statistical processes may be used in combination. Comparability refers to coherence across different time periods and geographical regions.

7.1 Geographical comparability

7.1.1. United Kingdom comparability

The road traffic estimates are produced for Great Britain (England, Scotland and Wales) and are aligned in terms of the definitions and coverage of the data. In addition, the data are given a similar set of validation checks to ensure the internal consistency of the data. Therefore, data can be compared at the national and sub-national level.

Northern Ireland Department for Infrastructure (DfI) does not produce summary road traffic estimates, and so can’t be compared with traffic estimates for Great Britain. DfI publishes traffic counts for the locations on the Northern Ireland road network that have permanent ATCs. These are available at: https://www.infrastructure-ni.gov.uk/publications/traffic-and-travel-information-incorporating-annual-traffic-census-and-variations

7.1.2. International comparability

Some comparisons can be made internationally, as most countries produce road traffic estimates. However, there are considerable differences in the data sources and methodologies used by different countries, as well as coverage and definitions. For example, the traffic estimates for Great Britain cover all vehicles travelling on roads, whereas some countries only capture the distance travelled by vehicles from the given nation.

7.2. Comparability over time

Each publication is internally consistent and provides timeseries back to 1993. Road traffic estimates are also published for the years 1949 to 1993, however, there is a break in the series at 1993, which is clearly explained in the relevant statistics.

In some years, there may be revisions to historic data points. Therefore, the most recent publication should be referred to for data for all years, and previous publications are archived on the road traffic statistics website.

7.3. Coherence – cross domain (sub-annual and annual statistics)

7.3.1. Coherence with Road Freight Survey data

Annual road freight statistics are based on survey data collected from freight operators, focusing on the volume and nature of goods transported. Differences in coverage, data sources, and definitions (e.g., vehicle classifications, trip purposes, or inclusion of foreign-registered vehicles) mean the figures will not align exactly to those presented in the road traffic estimates.

7.3.2 Coherence with National Travel Survey data

The National Travel Survey is a household survey that captures self-reported travel behaviour from a sample of individuals, focusing on personal trips rather than total traffic flow. As a result, the NTS may underreport certain types of travel and excludes non-resident and commercial travel. This means the results are not directly comparable to the road traffic estimates, even when reporting on the same modes of transport.

7.3.3. Coherence with Road Congestion and Travel Time data

The road congestion and travel time statistics focus on the average speed and delay experienced by users, typically derived from in-vehicle GPS data that track actual travel speeds and times on specific routes. As a result, the figures from these sources are not directly comparable to the road traffic estimates and may show different trends depending on the context.

7.3.4. Coherence with Public Service Vehicle Survey data (buses)

The annual bus statistics focus specifically on local bus services, typically operated under public service obligations, and exclude most coach travel. They are compiled from operator-reported data on passenger journeys, vehicle kilometres, and service provision. The differences in vehicle categorisation, data sources, and measurement focus mean the vehicle miles reported in the annual bus statistics are not directly comparable to the vehicle miles presented in the road traffic estimates.

7.3.5. Coherence - sub-annual and annual statistics

The publication Provisional road traffic estimates, Great Britain provides provisional traffic estimates for Great Britain by vehicle type and road type, and are based on the DfT ATC data source. Due to the methodology used to produce provisional traffic estimates, historic figures are subject to revision. However, these revisions are typically minor and will not affect qualitative patterns in the data. Provisional quarterly and annual traffic estimates for all motor vehicles have historically been accurate (typically within 1.5%) when compared with the final estimates.

The publication Daily domestic transport use by mode provides as an indication of traffic change on Great Britain’s roads, rather than actual traffic volumes. The data provided is indexed to the first week of February 2020 and the comparison is to the same day of the week. Therefore, 100 would mean that traffic is the same as the equivalent day in the first week of February 2020. In order to achieve a daily estimate of traffic change, lower levels of validation have been applied compared to the provisional and annual road traffic estimates. However, the daily data series has been verified against other sources and similar trends have been seen.

7.4. Coherence – internal

The statistics presented in this publication are internally consistent.

8. Accessibility and clarity

Accessibility refers to the ease with which users can access the statistics and data. Clarity refers to the quality and sufficiency of the commentary, illustrations, accompanying advice and technical details.

8.1. News release

Any press releases relating to this statistical publication have used the correct references.

8.2. Publication

The latest annual publication and accompanying data tables are available at: https://www.gov.uk/government/collections/road-traffic-statistics

The outputs are published in accessible formats. Statistical releases are available as html files, which are accessible for those who use assistive technologies. Data tables are available in ODS file format which can be accessed by using freely available software. The spreadsheets have been designed to be used easily by assistive technologies.

The statistical releases use plain language, in which technical terms, acronyms and definitions are defined where appropriate. The main findings are presented using a series of text and charts. Full details of the strengths and weaknesses of the data are provided at the end of each statistical report for users who are interested in this.

8.3. Online databases and micro-data access

The underlying data collected to produce the summary estimates is published alongside the annual release on a supplementary website roadtraffic.dft.gov.uk.

8.4. Documentation on methodology

This report provides detailed information about the methodology used to produce annual road traffic estimates. Additional technical reports are available from the road traffic statistics information page.

8.5. Quality documentation

The road traffic statistics information page contains:

• “Road traffic estimates: notes and definitions” has been published which outlines the coverage of the statistics as well as the key definitions

• Reports on the minor road traffic estimate review, including detailed descriptions of the minor road benchmarking methodology.

• Technical reports on methodology developments from the road traffic review that was published in 2018, which includes the work to develop the current stratification approach and other methodological and quality improvements.

9. Cost and burden

The costs associated with data collection and production, and respondent burden.

The department regularly reviews data collection methods and statistical methodology to ensure that customer needs continue to be met as efficiently and cost effectively as possible. Data collection contracts are competitively let to ensure value for money.

The data referenced in this statistical release is collected by observation. As such there is no respondent burden.

10. Confidentiality

Confidentiality refers to the procedures and policy used to ensure sound confidentiality practices.

The traffic counts themselves are not personal data, as the simple counts of vehicles by type do not include any information which could be used to identify an individual. However, in the course of carrying out the counts some personal data may be collected, for example traffic count videos may occasionally capture a registration mark, vehicle passenger or a distinctive vehicle. Therefore, strict controls are applied to minimise the incidental capture of personal information in the first place, and to the subsequent handling and processing of this information, to minimise the risk of it being disclosed or used inappropriately. The procedures used to protect confidentiality are set out in the DfT personal information and data protection in our statistics guidance.

All traffic data are held in secure databases. All data is stored, accessed and analysed using DfT secure IT systems. Data protection regulations are adhered to throughout the road traffic statistics production process, and access to data is controlled in accordance with departmental policy.

DfT adheres to the principles and protocols laid out in the Code of Practice for Statistics and comply with pre-release access arrangements. The pre-release access lists are available on the DfT website: Road traffic annual estimates: pre-release access.