Guidance

Road condition statistics - a basic guide and quality assessment

Updated 17 December 2024

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 of 31 March 2024, including roads owned and maintained by local highway authorities (also called local roads) and those owned and maintained by National Highways (also called trunk roads).

To note:

• the financial year ending March 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 rebranded as National Highways

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, 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 unless 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 derived 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.

How is road condition presented in the publication?

The main measure of road condition presented in the publication is the percentage of the network that should have been considered for maintenance that year, at local authority (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.

How is the National figure of condition calculated?

The percentage of red road for England is calculated by taking the percentage of red roads in each LA and multiplying this by the length of the LA network. The total length of red road is then used alongside the total network length for all LA’s who provided valid data to calculate an England estimate of road condition, percentage of red road.

Figure 1: Equation for calculating national figure of road condition

Where:

• %R National = Percentage of red road in England

• %R Local = Percentage of red road in a LA

• L Local = Kilometre length of road network in a LA

The network length data used is that from DfT Road Lengths in Great Britain.

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 2 of the Road condition statistics: 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 greater than or equal to 40 but less than 100 will not be in perfect condition but would still offer a good driving surface (called ‘amber’ condition). Anything scoring greater than or equal to 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 LA’s use RCI scores to identify which sections of road need repairing.

What parameters are used to calculate the RCI?

The following parameters are used to calculate the RCI:

• Rut depth (such as 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 2 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 and updated in April 2024.

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 stable 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 what we see nationally to be different on an LA level. You will be able to get some indication of this by looking at how your LA is performing in the LA level table.

The level of accuracy at which these statistics are published is to the nearest whole number as this is the lowest level of accuracy at which the data is provided. When assessing the change to unrounded figures, there have been gradual changes seen. As the local road network in England is nearly 300,000 kilometres, even small percentage changes account for fairly substantial sections of the road network.

It is also worth noting that collection and reporting of road condition data is only mandatory for the classified road network. Unclassified roads make up nearly two thirds of the network, but declaration of condition is voluntary, with surveys run over 4 years instead of 2 years, as done on classified roads. With the longer survey period in place, it is more likely that maintenance treatments or further worsening of condition will happen between surveys so data can be more out of date for unclassified roads.

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 LA’s 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 local 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, known as the Data Standard for Road Condition Monitoring. Published in September 2024, this specification outlines how data will be collected, processed and reported in the future.

Longstanding timeseries

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 three-year average, with information for the last two time periods presented (for example the average of ‘Financial year ending (FYE) 2016 to FYE 2018’ and the average of ‘FYE 2019 to FYE 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 LA’s whilst also making the categories clearer and simpler to allow more consistent reporting by LA’s.

Skidding resistance

Skidding resistance information on local roads was not published in 2022, 2023 and 2024, because the department are assessing the accuracy and comparability of this information between LA’s in England. There is currently no standardised regime for measuring skidding resistance apart from the use of SCRIM 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 LAs, 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 across London was stopped. This was a centrally managed contract by TfL, with data being sourced through Hammersmith and Fulham council. When the SCANNER surveys were stopped, London authorities were required to procure their own surveys independently of TfL. Between 2020 and 2022, the coverage of London in the release dropped substantially, and consequently surface condition figures for the region of London were not provided. In 2024, more data became available due to the resumption of TfL funding of ‘A’ road surveys in London, which also included data for 2023. This coincided with an increase in submissions of both ‘B’ and ‘C’ road data and unclassified roads data from London authorities, which has meant that figures for the London region are now provided.

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 LA’s in England and National Highways. Information from LA SCANNER surveys is currently processed through the UK Pavement Management System (UKPMS) system in each LA. 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 LA’s and National Highways. This contextual information is Traffic estimates from DfT and Maintenance Expenditure from the Ministry of Housing, Communities and Local Government (MHCLG).

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 potential issues are identified, LA’s 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 LA’s. Data is aggregated to produce regional and national figures; this is done using the road lengths published by DfT. National figures are calculated after excluding any LA’s 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 LA’s 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; for example, in 2023, 78% of LA’s provided valid data for ‘A’ roads (this increases to 85% when excluding London). In 2024, 95% of LA’s provided valid data for ‘A roads’, of which included all London authorities. DfT maximises the number of responses from LA’s through regular communication with LA’s via update emails, and attendance at regional groups and national conferences.

Calculations using Road Length Estimates

All calculations of national figures and the percentage of the road network receiving maintenance treatment uses information from DfT Road Length Estimates. Road condition data is presented as ‘A’ road, ‘B’ and ‘C’ Road combined, and Unclassified roads. The length of the ‘C’ and Unclassified road network is presented as a total in DfT road length estimates in most years. The length of these networks can currently only be accurately estimated individually when an R199b consultation is ran approximately every 4 years. As a result, The length of the ‘C’ and Unclassified networks are estimated each year for the purpose of producing a national figure for road condition. The proportion of road length which is ‘C’ road and Unclassified road is calculated from the latest figures where this is presented separately, these proportions are then applied to the latest combined ‘C’ and Unclassified road length. These figures are then used in further calculations.

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 LA’s 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 to which it refers.

Regarding punctuality, we adhere to the requirements of preannouncement 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 and comparable figure of road condition for the classified local road network in England. Despite the mandate, in recent years, a growing number of LA’s have been reporting road condition using alternative technologies that have unknown or lower levels of comparability to SCANNER surveys. DfT have written 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. The new Data standard for Road Condition Monitoring has now been published and will be implemented over the coming years.

Unclassified roads

There is currently 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 LA’s 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 more harshly than ‘B’ and ‘C’ roads, which are in turn marked more harshly 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 are required on the network, with ‘A’ roads tending to be a priority route for maintenance.

Skidding resistance

Skidding resistance information is collected from LA’s and National Highways each year. For LA’s, 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 LA. This inconsistency between LA’s limits the comparability between LA’s, and also our ability to create a robust national figure. For these reasons, DfT have not published skidding resistance data in 2022, 2023 and 2024 (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 the percentage of roads requiring maintenance (red) to DfT. 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 road 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 road 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.

LA’s

Data for surface condition indicators has been published annually since 2008. New LA’s 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 LA codes are used as standard throughout, which allows this information to be linked to other LA 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 trunk motorways and trunk ‘A’ roads in England. Roads that are managed by LA’s 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 the road lengths release covers Great Britain and uses 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 tables 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 and 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 LA’s

There is an additional trade-off when accepting data from LA’s which have only surveyed a small proportion of their road. It is desirable to accept as much data from LA’s as possible in order to increase the coverage of the national figures. However, DfT cannot publish data from LA’s 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 LA’s in order to strike a sensible balance between these aims.

Future road condition statistics publications

As noted above, the department has been working on a new 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. In September 2024, DfT published PAS 2161: Road condition monitoring (RCM) data Specification. DfT has worked with the British Standards Institute, Transport Research Laboratory, LA’s, and a wide variety of industry experts to develop a new approach for road condition monitoring data.

To ensure data quality, accuracy, and comparability, prospective RCM technologies will be required to undergo an approvals process to demonstrate that they can meet the PAS requirements, which will benchmark the results of surveys from RCM technologies alongside highway engineers.

The new standard will move away from the current red, amber and green categorisation of condition, to 5 more detailed categories. These new categories were designed in collaboration with LA’s and technology companies and are based on the amount of potential treatment required to return the carriageway to a satisfactory condition. This new categorisation of condition will not directly map to the percentage of red, amber and green roads, so there will be a break in the time series of this statistical series. To mitigate the impact of this change, DfT are planning to dual run the standards in 2025 and 2026, with a move to the new reporting specified in PAS 2161 in 2027.

If you have any questions, please email [email protected].