Guidance

Road conditions: notes and definitions

Updated 23 November 2023

Applies to England

Introduction

This publication supports the latest statistics on the condition of roads in England, as well as other aspects of highways maintenance.

It is part of road network size and condition series. Detailed data tables are available from the website.

For a more detailed commentary on road condition statistics, see the annual release.

This note provides definitions used for road condition statistics. It also includes useful information on the source of the data.

Data source

The statistics come from a variety of sources:

SCANNER surveys

These are automated surveys carried out using SCANNER vehicles. Local authorities commission them to assess the surface condition of their ‘A’, ‘B’ and ‘C’ road network and in some cases on their unclassified (‘U’) road network as well.

TRACS surveys

These are automated surveys carried out using automated vehicles. They are used to assess the surface condition of the trunk ‘A’ and motorway network in England. These roads were managed by the Highways Agency until April 2015, when they were replaced by Highways England, who were replaced in September 2021 by National Highways.

Coarse and Detailed Visual Inspections (CVI and DVI)

These are manual visual inspections used to assess road surface condition. They are used on local authorities’ unclassified road network, but some authorities also use them on their classified network.

Prior to April 2012, statistics on unclassified roads were collected by the Association of Directors of Environment, Economy, Planning and Transport (ADEPT, formerly the County Surveyors’ Society). These are now collected via DfT’s road condition surveys alongside statistics for classified roads.

Skidding resistance survey

Used by local authorities and National Highways (formerly Highways England and previously Highways Agency), skidding resistance is a measure of the road surface contribution to the frictional forces developed between a vehicle’s tyres and the road when accelerating, braking or cornering. LA results are presented as 3-year averages as it is common practice for authorities to survey their principal road network over 2 or 3 year cycles. Trunk roads are surveyed for skidding resistance every year. Local-authority level skidding resistance data was not reported in the 2022 publication, and is not reported in the 2023 publication, The Department for Transport are currently reviewing how this data is being reported to ensure the quality and accuracy of this information. This means that table RDC0140 is not published in this year’s publication.

Road maintenance treatments and categories have been updated in 2023 reporting to include more up-to-date definitions and allow greater consistency across local authority reporting of this data. From 2023 onwards, work done will be reported as follows:

Strengthening, consisting of reconstruction excluding in-situ recycling, and in-situ recycling,

Resurfacing, consisting of resurfacing, overlay, and thin surfacing,

Preservation, consisting of surface dressing, micro surfacing, and preservation and rejuvenation.

This change in reporting should better reflect current maintenance treatments. The data presented for the categories of maintenance treatments on local roads for previous years up to 2022 will still reflect the previous maintenance treatment categories and is therefore not directly comparable to 2023 and future years. The affected tables in the publication are RDC0320 and RDC0321.

More details on each of the survey methods are provided in the Technical Note.

Definitions

Road Condition Indicator (RCI)

SCANNER surveys measure a number of parameters at 10-metre sections along the road. The outputs from the measured parameters can be combined to produce a single figure giving an indication of the surface condition at that specific location. See Sections 3.4 and 3.5 in the Technical Note for details on the parameters measured and how they are used, and Section 3.6 for how the parameters are used to calculate an RCI value.

RCI outputs are scored between 0 and 315. Scores between 0 and 40 indicate that the observed road section is in good condition. This category is referred to as ‘green’ or ‘good’. Scores over 40 but below 100 indicate that the location is showing some deterioration and should be investigated to see if the road needs treatment. This category is referred to as ‘amber’. Any road sections scoring 100 or higher are likely to show considerable deterioration and may need maintenance within the next 12 months. This category is referred to as ‘red’ or ‘poor’.

The proportion of the network that is ‘red’ is reported to DfT by local authorities via Single Data List items in the road condition surveys that are sent to authorities each year. These figures are presented in table RDC0120 and are used to produce the regional and national figures that are presented in RDC0121.

Road network and classification

A full set of definitions and descriptions about the road network are available in the Technical Note.

Specific issues

COVID-19

The collection process was postponed for LAs for the April 2019 to March 2020 reporting period due to the pressure and resource challenges they faced due to the coronavirus outbreak. Although road maintenance did continue, this may have been affected due to changes in local authority priorities during the outbreak. The data for both reporting periods (April 2019 to March 2020 and April 2020 to March 2021) were collected during Summer 2021.

London data

How London surveys have been carried out has changed, which has resulted in lower coverage of London than in previous years.

Potholes

A SCANNER vehicle does not specifically record potholes. Instead, it would identify that there is surface damage and deterioration on that section of the road, according to the parameters that it measures.

Therefore, although the statistics are unable to provide information about the number and size of potholes, any road section which has potholes is likely to get a high RCI score. Similarly, any road section with a high RCI score is likely to have a wide range of deterioration, possibly including potholes.

Winter damage

SCANNER surveys are carried out on a financial year cycle, with each local authority aiming to survey set proportions of their road network between April and March each year. Local authorities will seek to survey at least 45% of their ‘A’ road network and 42.5% of their ‘B’ road network in each direction every year and 40% of their ‘C’ road network in one direction every year.

As SCANNER surveys are mounted on vehicles and use lasers to scan the road surface, surveys cannot take place when snow, ice or standing water is on the road. This means that a significant proportion of the surveys take place between May and October each year.

The result of the survey timing is that damage from severe winter weather, as happened, for instance, in the winter period of December 2010 to February 2011 and December 2013 to February 2014, may not be picked up until the following year. In addition, any severe damage might be repaired before the surveys start, so it is possible that such severe damage is never recorded by SCANNER vehicles if it occurs and is repaired within the same year.

Statistical conventions

Units

Figures are shown in italics when they represent percentages, indices or ratios

Rounding of figures

In tables where figures have been rounded to the nearest final digit, there may be an apparent discrepancy between the sum of the constituent items and the total shown.

Conversion factors:

1 kilometre = 0.6214 mile

1 billion = 1,000 million

Symbols:

[x] = no submission sent

[y] = invalid submission due to insufficient surveying

[z] = not applicable

0 = nil

or _ = break in the series

[r] = revised

Glossary of technical terms

More detailed explanations of some of the terms can be found in the Technical Note.

Annual Engineers Inspection (AEI)

This is a visual survey method that is carried out by engineers. It is outcome based i.e. focuses on the type of treatments (if any) that are required for a given section of road. Because it does not give an overall indicator of road quality that is comparable to other methods, it is not currently included in the data. However, some local authorities are increasingly using it to help them make decisions on road maintenance.

Best Value Performance Indicator (BVPI)

BVPIs showed the relative performance of English local authorities for different aspects of performance. These were introduced in April 2001 and were last reported for April 2008. They were replaced by the National Indicator Set which came into effect from April 2008. This in turn was replaced by the Single Data List from April 2011.

Carriageway

The paved area of the highway carrying vehicular traffic and including any hard shoulders and marginal strips.

Classified roads

Local authority owned and maintained roads with ‘A’, ‘B’ or ‘C’ classification. Note that in the report’s tables and figures, the term ‘principal roads’ refers to local authority ‘A’ roads, and the term ‘classified roads’ refers to local authority ‘B’ and ‘C’ roads. Local authority ‘A’, ‘B’ and ‘C’ roads account for around 40% of the local authority road network.

Characteristic SCRIM Coefficient (CSC)

An estimate of the underlying skid resistance once the seasonal variation has been taken into account.

Coarse Visual Inspection (CVI)

A method of inspecting road condition at network level developed as part of the UK Pavement Management System (see below). Fewer defect details are recorded than from a DVI (see below), but a CVI may be carried out either from a moving vehicle or as a walked survey. A CVI provides information on road condition at the local authority network level and identifies sections of road where a more detailed DVI survey may be required to more accurately determine the appropriate maintenance treatment.

Design, build, finance and operate (DBFO)

Detailed Visual Inspection (DVI)

A method of inspecting road condition developed as part of the UK Pavement Management System (see below). A DVI is carried out by one or more inspectors walking along the road. The method is often used after initial problems have been noted during a CVI survey but some local authorities prefer to use walked DVI surveys, particularly where footway condition is important.

Footway

Any area alongside a road intended for use by pedestrians. (Colloquially a footway will be described either as a ‘pavement’ or as a footpath alongside a road.)

GAIST

A company providing video-based methods of inspecting road condition which can produce full and part detailed network condition maps and presents its findings to LAs in a different manner to SCANNER. It is increasingly being used by LAs on Classified and Unclassified roads to help them make decisions on road maintenance.

Highways Agency Pavement Management System (HAPMS)

A generic term to cover the computer systems and related engineering and business processes that comprise the Highways Agency Pavement Management System.

In-situ recycling

Re-using of the existing construction in-situ, with the addition of foamed bitumen, bitumen emulsion and cement. Includes shallow (retread), medium (for example, regen), and deep in-situ recycling, with a Surface Dressing or asphalt surface course finish.

Investigatory level

The level of condition at which consideration is given to the need for maintenance. At this juncture, all available evidence (for example, accident rates) would be taken into account.

Local roads

Local authority maintained ‘A’, ‘B’, ‘C’ and unclassified roads. These are also known as non-trunk roads.

Mean Summer SCRIM coefficient

Mean of 3 or more SCRIM Coefficients measured for a length of road at well-spaced intervals between May and September in a year.

Micro surfacing

A site-mixed, cold-applied (more eco-friendly) asphalt surface course; an alternative to hot asphalt (surface dressing).

Motorway

A particular type of road with restricted use, carrying predominantly long-distance traffic. Most motorways are the responsibility of Highways England (formerly the Highways Agency) but there are some short lengths of local authority motorways.

Non-trunk roads

Local authority maintained ‘A’, ‘B’, ‘C’ and unclassified roads. These are also known as local roads.

Non-principal roads

Local authority maintained ‘B’, ‘C’ and unclassified roads

Overlay

Material placed on top of the existing pavement in a layer (or layers) of regular thickness. This is a more substantial treatment than a surface dressing.

Pavement

Technical term for the surface of a road. Note this is not restricted to a footway (see definition above).

Preservation and rejuvenation

Cost-efficient road surface treatment, consisting of either a spray-applied, penetrative preservative or a rejuvenator that penetrates and changes the rheology of the binder (for example, bitumen).

Principal roads

Local authority maintained ‘A’ roads and motorways. In general, they carry less traffic than all-purpose trunk roads which are ‘A’ roads and motorways owned and maintained by central government.

Road Conditions in England (RCE)

Refers to this bulletin.

SCANNER Road Condition Index (RCI)

Indicates the condition of the road where a low score represents a road in ‘good’ condition whilst a high score represents a road that needs further investigation or where maintenance should be considered, as surveyed by SCANNER.

Reconstruction excluding in-situ recycling

The removal of some or all of the structural layers of a road pavement and their replacement with new material, including a new surfacing. This is a more substantial treatment than overlay.

Resurfacing

The removal and replacement of the existing surface, in order to restore the running surface and improve surface characteristics.

Rural roads

Roads that are not in settlements with a population of 10,000 or more.

Surface Condition Assessment of the National Network of Roads (SCANNER)

Vehicle-mounted automated carriageway surface condition surveys for local authority roads, developed from the TRACS surveys used on the trunk road network. Like TRACS, the specification covers the requirements for both the machinery used and the survey process.

Sideway-force Coefficient Routine Investigation Machine (SCRIM)

A lorry-based machine that when driven over a pavement surface, measures the resistance to skidding of the wet pavement surface.

Single annual SCRIM survey

All of lane 1 of the network is surveyed once during the SCRIM testing season in each year. In successive years, each road length is tested in the early, middle and late parts of the season.

Site (NRMCS)

100 metres of carriageway and associated footways and verges identified by DfT (for inspection by local authorities and - up to 2002 - by trunk road agents) to provide the visual condition for analysis by DfT. The sites are selected from a random sample of all roads (except motorways) in England and Wales. NRCMS surveys have not been carried out since April 2006.

Standard axle

A single axle with 2 wheels and carrying a load of 80kN. The life of a pavement that will carry different axle types and loads is expressed in terms of the number of standard axles the pavement will carry.

Surface dressing

A single, double or triple layer of aggregate combined with one or more layers of binder (for example, bitumen) to form a running surface. This may be laid over the existing surface.

Thin surfacing

Thin surfacing systems are machine-laid proprietary mixes of asphalt that have the capability to regulate the surface profile of a road pavement, restoring surface texture and skid resistance. They have thicknesses up to 40 millimetres (mm).

Traffic Speed Condition Survey (TRACS)

A label to describe a methodology for National Highway’s machine-based surveys of surface condition, including cracking and rutting, of the trunk road network in England. The TRACS specification covers the requirements for both the machinery used and the survey process.

Trunk roads: Motorways and all-purpose trunk roads owned by central government and for which National Highways (in England) and the Welsh Government (in Wales) have responsibility for maintenance and operation. These are strategic roads with a high proportion of long-distance traffic although some trunk roads may also have lengths, with the same number, designated as an ‘A’ principal road, where traffic is predominantly local in nature.

TRACS type surveys (TTS)

United Kingdom Pavement Management System (UKPMS)

This is a standard logical design for software used by local highway authorities for the management of the maintenance of their road networks. A number of companies’ market software that meets the UKPMS requirements. Associated with UKPMS are standard survey types (CVI and DVI surveys, see above) and standard ‘rules and parameters’ to be used when processing survey data for ‘national’ purposes (for Single Data List items).

Unclassified roads

Minor roads which are not designated as classified roads and which are owned and maintained by a local highway authority. By length, some 60% of the local authority network is unclassified.

Urban roads

Roads in settlements with a population of 10,000 or more.

Vaisala

A company providing a method of inspecting road condition at network level combining the use of Artificial Intelligence and video data. This is a newer method of data analysis which is being used by a few LAs.

XAIS

A company providing multiple methods of inspecting road condition, using video, Artificial Intelligence and AEI. These are newer methods of data analysis which are being used by a few LAs.