Guidance

Road condition statistics - a basic guide and quality assessment

Updated 23 November 2023

Applies to England

Section 1: Basic guide to road conditions

What is the purpose of the Road Conditions in England statistical bulletin?

Road Conditions in England (RCE) provides information about the overall state of roads in England as well as an indication of whether the condition is improving or worsening.

What roads does it provide information about?

Information is provided about all types of roads maintained at public expense in England as at 31 March 2021, including roads owned and maintained by local highways authorities (also called local roads) and those owned and maintained by National Highways (also called trunk roads).

To note:

The financial year 2014 to 2015 was the last year of reporting by the Highways Agency, after which it was replaced by Highways England from April 2015 onwards.

In August 2021, Highways England was re-branded as National Highways. As the latest reporting period was prior to the change happening, this has meant that in the statistical release, we still refer to them as Highways England.

How do you measure road condition?

There are a number of ways of measuring road condition, depending on which aspect of the road is of interest. Most of the information in RCE is about the surface condition of the road. For example, how many defects there are, and whether the surface is breaking up. Surface condition surveys can be carried out either manually, by a surveyor visually inspecting the road, or automatically, using vehicles with mounted lasers and cameras to measure different aspects of the road.

Apart from unclassified roads, all the information on the surface condition in RCE comes from automated surveys except where stated otherwise. The machines that carry out the surveys on the local roads are called SCANNER (Surface Condition Assessment for the National NEtwork of Roads) and the machines which survey trunk roads are called TRACS (TRAffic-speed Condition Survey). The two approaches have many similarities, with SCANNER obtained from the TRACS approach.

SCANNER, TRACS and the other techniques are discussed in more detail in the Technical Note. Other techniques are used to assess the condition of the sub-surface of the road or the ‘skiddiness’ of the road.

What is the main way road condition is shown in the publication?

The main measure of road condition shown in the publication is the percentage of the network that should have been considered for maintenance that year, at LA, regional and national level. This is the percentage of its network that an LA or National Highways calculated to be in “red” condition based on its Road Condition Indicator (RCI) score.

What is the Road Condition Indicator (RCI)?

The Road Condition Indicator (RCI) is used to assess the condition of individual sections of road. It is calculated using the outputs from the surveys mentioned above. A complete description and worked example of RCI is provided in Section 3.6 of the  Technical Note.

An RCI score can range between 0 and 315. Any stretches of road scoring below 40 are declared to be in good, or ‘green’, condition. Any stretches scoring higher than 40 but less than 100 will not be in perfect condition but would still offer a good driving surface (called ‘amber’ condition). Anything scoring over 100 is likely to be in poor condition and will probably need maintenance within in the next year or so (called ‘red’ condition). Highways engineers in local authorities use RCI scores to identify which sections of roads need repairing.

What parameters are used to calculate the RCI?

The following parameters are used to calculate the RCI.

Rut depth - the depth of the ruts running along the length of the road caused by where the wheels of vehicles drive.

Bumpiness along the road surface (called longitudinal profile).

Texture of the road surface.

Cracking of the road surface.

More complete descriptions and photographs of roads showing some of these defects can be found in Section 3.4 of the Technical Note.

How many potholes are in the roads?

SCANNER surveys cannot identify potholes as a specific defect. However, they do not ignore potholes completely. Potholes can show up as defects under the measured parameters, and so will contribute to the condition of the road.

Similarly, it is not possible to tell how much larger the potholes are in different years. There are, however, other measures that have been developed within the sector that focus more specifically on potholes. This includes the RAC pothole index, which is based on the number of callouts from their members that are related to vehicle faults that are likely to have been caused by a pothole.

The information from the latest ‘RAC Pothole Index’ was published in 2023.

There are also a growing number of tools that allow the public to report potholes and road defects through the use of mobile apps.

The statistics suggest that roads are getting better yet there are more potholes on my street now than there used to be. How can this be?

The statistics give an indication at what is happening on average, throughout the country. It is possible for the national condition to improve but your own local authority’s roads to get worse. You will be able to tell this by looking at how your local authority is performing in the LA-level table.

Even if your local authority has seen improvements overall, this does not necessarily mean that every road is improving. It is likely that some roads will have worsened even in an authority which is improving overall.

Section 2: Quality Assessment

Relevance

Uses of data

Road condition statistics include key performance indicators for the state of the nation’s roads. The information published is used by the DfT to inform spending review allocations of funding to local authorities for highway maintenance, as well as providing transparency to local government, parliament, and the public.

Meeting users needs

Road condition statistics includes information on the condition and maintenance of roads maintained at public expense in England, for both locally-managed roads and roads which are centrally-managed by National Highways. This data is clearly defined and there is extensive documentation published to accompany the statistics.

It is intended that all these statistics will be continually reviewed to consider user needs. There is an ongoing project to increase the amount of information available on road condition in England.

Longstanding time series

This publication provides information on the condition of England’s roads back to the year ending March 2008. It also provides information on the maintenance work done in England back to the year ending March 1985. The skidding resistance information published alongside these statistics is done so on a rolling 3-year average, with information for the last two time periods presented (for example, the average of 2015 to 2016 to 2017 to 2018 and the average of 2018 to 2019 to 2020 to 2021). The statistics are broken down by multiple classifications to allow a wide range of user needs.

Maintenance

The publication also presents information on the proportion of road length receiving maintenance treatment each year. How this information was reported was reviewed in 2023 under the guidance of the Road Surface Treatment Association (RSTA). This review modernised the treatment options in the annual survey sent to local authorities whilst also making the categories clearer and simpler to allow more consistent reporting by local authorities.

Skidding resistance

Skidding resistance information on local roads was not published in 2022 and 2023, because the department are assessing the accuracy and comparability of this information between local authorities in England. There is currently no standardised regime for measuring skidding resistance apart from the use of SKRIM technology, which does not provide robust comparable data in the current format.

The department will take forward work to make robust skidding data available for users. However, this will require resource from both the Department of Transport and local authorities, and so this will be addressed after completing the data standard for road condition monitoring data (see below), because this is of higher priority to our users.

Data for London

In 2020, the regime of SCANNER surveys to collect local road condition data across London was stopped. This was a centrally-managed contract by TfL and was carried out through Hammersmith and Fulham council. When the SCANNER surveys were stopped, London authorities were required to procure their own surveys independently of TfL and report this data to the Department for Transport. Compliance was limited, and between 2020 and 2023 the coverage of London in the release dropped substantially. As new surveys are being procured and TfL have begun a new regime of non-SCANNER surveys coverage should increase in the future.

To ensure that the low coverage in London does not have a significant impact of the national figure, the national figure has been presented including and excluding data for London. The relatively small size of London’s road network compared to the rest of the country means that the lack of data for London is unlikely to skew national figures for road condition.

Road classification

The statistics are reported by road classification; ‘A’, ‘B’, ‘C’ and ‘Unclassified’ roads. ‘B’ and ‘C’ roads are combined in the statistics as this matches up to how maintenance funding formulas are set.

Accuracy and reliability

Data process

Quality assurance:

Data is collected annually via surveys to all local authorities in England and National Highways. Information from local authority SCANNER surveys is currently processed through the UK Pavement Management System (UKPMS) system in each local authority. The accuracy of UKPMS systems is checked through accreditation and annual compliance checks. The information from this system is then declared in the DfT survey alongside other information from their asset management systems. Contextual information is presented alongside the information collected from local authorities and National Highways. This contextual information is Traffic estimates from DfT and Maintenance Expenditure from DLUHC.

SCANNER survey data is collected by accredited suppliers, and their data is quality assured annually by the Transport Research Laboratory, with standards overseen by the Road Condition Management Group (RCMG) which is made up of sector experts. Once data is reported to DfT it goes through rigorous validation and quality assurance against existing data. Where potentially issues are identified, local authorities are contacted to revise the data or to provide contextual information.

Excluding invalid data

The majority of figures presented in this release are directly reported from local authorities. Data is aggregated to produce national figures, this is done using the road lengths published by DfT. National figures are calculated after excluding any Local Authorities which have provided invalid data. Therefore, if 130 authorities provided valid data, the national figure will be calculated using the road lengths of these 130 authorities only.

Response rates

Not all local authorities provide road condition data to the DfT so there is a risk that these statistics could be affected by a non-response bias. However, data coverage is relatively high with, for example, in 2023, 78% of local authorities provided valid data for ‘A’ roads (this increases to 85% when excluding London). DfT maximises the number of responses from Local Authorities through regular communication with local authorities via update emails, and attendance at regional groups and national conferences.

Timeliness and punctuality

The information that feeds into the Road Condition statistics publication is collected on a financial year basis, from April to March. Collection of this information from local authorities and National Highways begins in May each year. The information from surveys is not delivered instantly to authorities so time is given to ensure authorities will have the information they need to fulfil the DfT request for data. The data undergoes a rigorous validation and quality assurance process before it is processed and published in autumn of each year. The data is normally released within 6 to 8 months from the time period that it refers to.

Regarding punctuality, we adhere to the requirements of pre-announcement of publication.

Comparability and coherence

Standardised data

Road condition data for local roads

Currently, DfT requirements mandate the use of SCANNER technology to provide a consistent comparable figure of road condition for the entirety of the local road network in England. Despite the mandate, in recent years a growing number of local authorities have been reporting road condition using alternative technologies that have unknown or lower levels of comparability to SCANNER surveys. DfT are writing a new road condition monitoring data standard to ensure comparability of information from multiple technologies, with an aim of a more accurate representation of the condition of England’s roads.

Unclassified roads

There is no prescribed technology to use on Unclassified roads and the required level of coverage is around half of what is expected for the classified network, with data collected over a 4-year period for Unclassified roads as opposed to the 2-year period for classified roads. Surveys on Unclassified roads are more likely to be manual rather than automated surveys like SCANNER. Due to the factors outlined above the comparability of the Unclassified road data between local authorities is lower than the classified network where the majority use SCANNER.

Road classification

SCANNER survey results are weighted depending on the road classification. A roads are marked harsher then B and C roads which are in turn marked harsher than Unclassified roads. This means that the information presented by road classification isn’t directly comparable, but this data is primarily used as an indication of where maintenance treatments a required on the network, with A roads tending to be a priority route for maintenance.

Skidding resistance

Skidding resistance information is collected from local authorities and national highways each year. For local authorities there is no set regime of how this is carried out, and therefore coverage and the level at which further investigation is required is set by the local authority. This inconsistency between local authorities limits the comparability between local authorities and also our ability to create a robust national figure. For these reasons, DfT have not published skidding resistance data in 2022 and 2023 (see above). National Highways have a consistent approach across their network and this information has always been presented separately to the data for local roads as National Highways roads are held to different standards and KPIs to local roads.

Centrally-managed versus locally-managed roads

National Highways also report to DfT the percentage of roads requiring maintenance (red). This figure is produced from a TRACS survey which is similar to SCANNER technology but has some differences.. National highways report the percentage of red roads as those classified as red in TRACS surveys minus the amount receiving maintenance treatments. This means that the metric for road condition from national highways takes into account maintenance work done after the survey was carried out whereas local roads are reported as at the point of survey with no adjustments. The difference in this definition is clearly stated. Additionally, for local roads, the percentage of red roads is purely derived from the data produced by the SCANNER surveys, therefore is not comparable to the National Highways figures.

Maintenance

The improvement to maintenance data explained above will mean an unavoidable break in the time series when assessing changes in the amount of specific maintenance types, but will not affect the total amounts for overall maintenance work.

Local authorities

Data has been published annually since 2008. New local authorities are created periodically, generally as a joining or separating of existing lower tier authorities. This results in breaks in the time series for some authorities. ONS local authority codes are used as standard throughout, which allows this information to be linked to other local authority data.

Difference to other publications

This publication refers to roads that are managed by National Highways as the Strategic Road Network (SRN), which is made up of motorways and trunk roads in England. Roads that are managed by local authorities are referred to as local roads. This is consistent with the statistics published on road traffic, but is inconsistent with the definitions used in the road length statistics release. This difference is because of differences in the geographical coverage of the two releases. Road condition reports on England only whereas road lengths covers Great Britain and use the more universal terms of trunk and principal.

Accessibility

This publication complies with the latest GOV.UK and Government Statistical Service requirements for accessibility at the time of publication. Statistical releases and accompanying methodology documents are published in HTML format and data tables are available in ODS format. There is consistent use of alternative text throughout the statistical release.

Clarity

The published tables maintain consistent terminology, in recent years some definitions have changed to allow for more consistency with other output from DfT. The format of table varies minimally between publications, except where accessibility guidelines require tables to be altered. Language in the statistical release is chosen to be plain and clear whilst retaining technical terms.

Trade-offs

Non-SCANNER road condition data for local roads

Currently, data from non-SCANNER technologies is accepted. The data is fitted to match the red, amber and green categories of SCANNER but is not directly comparable. The data is accepted to give greater coverage to give a more accurate national picture of road condition. To mitigate the reduced comparability, the new data standard for road condition monitoring aims to get comparable data from multiple survey types, as referenced above. Therefore, once the standard is in place the data comparability should improve. The time between data collection and publication is used to validate the data, with thorough checks and improvements carried out to result in robust and trustworthy statistics.

Data coverage within local authorities

There is an additional trade-off when accepting data from Local Authorities which have only surveyed a small proportion of their roads. It is desirable to accept as much data from local authorities as possible in order to increase the coverage of the national figures. However, DfT cannot publish data from local authorities where their data coverage is too low because this could provide a misleading picture of the road condition in that authority. The DfT carefully sets consistent and appropriate thresholds for accepting data from local authorities in order to strike a sensible balance between these aims.

Future road condition statistics publications

The department have been working on a ‘data standard for road condition monitoring’ since 2020. This will look to improve comparability of data, standardise how data is reported independent of technology used, and provide increased clarity of reporting.

If you have any questions, please email road maintenance statistics.