Guide to severity adjustments for reported road casualties Great Britain
Updated 30 July 2026
© Crown copyright 2026
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Background on the introduction of injury-based reporting
The Department for Transport (DfT) publishes road casualty statistics based on the STATS19 data collection system. This system sets out the variables and data standards that police forces in Great Britain use to report road collisions involving personal injury.
Within STATS19, injured casualties are classified as either seriously or slightly injured. Historically, this classification was based on the judgement of the recording police officer, using an agreed definition of serious injury (outlined in our notes and definitions).
In recent years, many police forces have adopted injury-based reporting systems (IBRS). Under these systems, officers record the injuries sustained by a casualty from a predefined list and overall casualty severity is determined from the most severe injury recorded. This reduces the level of judgement involved in severity coding and provides more detailed information on injury outcomes.
Following a recommendation in the 2018 STATS19 review, all forces are expected to move to injury-based reporting. By the end of 2025, 39 of 44 police forces in Great Britain had adopted an injury-based reporting system, meaning that most reported road casualties are now recorded using this approach.
However, the introduction of injury-based reporting has affected the level and trend of reported serious casualties. To ensure figures remain comparable over time and between areas, DfT, with the help of the Office for National Statistics, has developed a methodology to estimate the number of serious casualties that would have been recorded if all police forces had used injury-based reporting systems. These adjusted figures are now used in the published national statistics and are particularly important when analysing data that combine injury-based and non-injury-based reporting systems.
This guidance explains how injury-based reporting systems work, how severity adjustments are produced, and when adjusted figures should be used.
Definitions
IBRS: Injury Based Reporting System. A system used by police to record collision data, where casualty injuries are recorded and casualty severity then coded from the most severe injury. CRASH and COPA are examples.
CRASH: Collision Recording and Sharing system. This is a centralised system used by many police forces to record road traffic collisions.
COPA: Case Overview Preparation Application. This is a system used by the Metropolitan Police Service to record road traffic collisions.
Classification of injury severity within injury-based reporting systems
In injury-based severity reporting systems (such as CRASH and COPA), the reporting officer records all injuries for the casualty. The injuries are then automatically converted to a severity level from ‘slight’ to ‘serious’ and the most serious severity is used to identify the casualty severity.
A list of the injuries from which police officers can select, and how these map to different overall severities, is shown in Table 1 and illustrated Figure 1.
Table 1: Classification of injury severity using injury-based reporting systems (such as CRASH or COPA)
| Injury | Detailed severity | Severity classification |
|---|---|---|
| Deceased | Killed | Killed |
| Broken neck or back | Very Serious | Serious |
| Severe head injury, unconscious | Very Serious | Serious |
| Severe chest injury, any difficulty breathing | Very Serious | Serious |
| Internal injuries | Very Serious | Serious |
| Multiple severe injuries, unconscious | Very Serious | Serious |
| Loss of arm or leg (or part) | Moderately Serious | Serious |
| Fractured pelvis or upper leg | Moderately Serious | Serious |
| Other chest injury (not bruising) | Moderately Serious | Serious |
| Deep penetrating wound | Moderately Serious | Serious |
| Multiple severe injuries, conscious | Moderately Serious | Serious |
| Fractured lower leg or ankle or foot | Less Serious | Serious |
| Fractured arm or collarbone or hand | Less Serious | Serious |
| Deep cuts or lacerations | Less Serious | Serious |
| Other head injury | Less Serious | Serious |
| Whiplash or neck pain | Slight | Slight |
| Shallow cuts or lacerations or abrasions | Slight | Slight |
| Sprains and strains | Slight | Slight |
| Bruising | Slight | Slight |
| Shock | Slight | Slight |
Figure 1: Mapping of historic serious and slight categories to injury-based classification of severity
Additional information available from injury-based reporting systems
In addition to determining whether a casualty is recorded as killed, seriously injured or slightly injured, injury-based reporting systems provide two pieces of information which were not previously available from most police-reported road casualty records:
- a more detailed severity classification, distinguishing between very serious, moderately serious and less serious injuries
- the most severe injury sustained by the casualty
This information allows a more detailed understanding of the outcomes of road collisions than is possible using the traditional serious/slight classification alone. For example, it enables analysis of the types of injuries sustained by different road user groups and the composition of serious casualties. Examples of how these data are used are included in the annual road casualty publication, and for earlier years in the injury severity factsheets.
Coverage of detailed injury information
Detailed injury severity and injury type information are only available from police forces using injury-based reporting systems. As the adoption of these systems has increased over time (as shown in Table 2 below), the coverage of detailed injury information has also expanded.
Users should note that analyses based on detailed injury severity or injury type may not represent all reported road casualties in Great Britain, particularly for earlier years when fewer police forces were using injury-based reporting systems. The proportion of casualties covered by injury-based reporting systems should therefore be considered when interpreting these statistics. Where detailed injury severity or injury type statistics are published, information will be provided on the police forces or casualty coverage included within those analyses.
In addition, the quality and completeness of detailed injury information can vary between police forces and over time. For example, some police force data have been excluded from particular injury-type analyses where a high proportion of injuries were recorded in non-specific categories or where severity and injury classifications were inconsistent.
Adoption of injury-based reporting by forces
Table 2 shows the police forces which use or have used either CRASH, COPA or other injury-based reporting systems and the dates from which these systems have been used. Note that adoption dates are indicative as there can be phased introduction of new systems during transitions. By the end of 2025, 39 of 44 forces had adopted injury-based reporting:
- Approximately half of English police forces adopted the CRASH system for recording reported road traffic collisions at the end of 2015 or the first part of 2016, although Surrey has been using the system since November 2012.
- The Metropolitan Police Service (MPS), which has the most casualties of any force, switched to a new reporting system called COPA (Case Overview Preparation Application), which went live to police officers from November 2016.
- In 2019, 10 police forces adopted CRASH. This includes all the Scottish police forces, Sussex and Lancashire. In 2021 Greater Manchester, West Yorkshire and Nottinghamshire joined CRASH, and in 2022 Dyfed-Powys became the first Welsh force to move to CRASH, with Wiltshire adopting it during 2025.
- During 2024 and 2025, some non-CRASH forces moved to injury-based reporting, as shown in the table.
As at July 2026, further forces have already adopted IBRS during 2026 (including North Yorkshire ), or have plans to do so, whether through a change of reporting or by adopting an IBRS-system such as CRASH. It is expected that by the end of 2026, the only forces not using IBRS systems will be Lincolnshire and North Wales.
Table 2: Adoption dates for CRASH or COPA by police force (to end 2025)
| Police Force | System Used | Adoption Date |
|---|---|---|
| Surrey | CRASH | November 2012 |
| South Yorkshire | CRASH | January 2013 |
| Staffordshire | CRASH | May 2015 |
| West Midlands | CRASH | November 2015 |
| Warwickshire | CRASH | November 2015 |
| Essex | CRASH | November 2015 |
| City of London | CRASH | November 2015 |
| Gloucestershire | CRASH | November 2015 |
| Metropolitan Police Service | COPA | November 2015 |
| West Mercia | CRASH | December 2015 |
| Devon and Cornwall | CRASH | December 2015 |
| Cumbria | CRASH | January 2016 |
| Humberside | CRASH | January 2016 |
| Kent | CRASH | January 2016 |
| Norfolk | CRASH | February 2016 |
| Suffolk | CRASH | February 2016 |
| Durham | CRASH | March 2016 |
| Northumbria | CRASH | April 2016 |
| Bedfordshire | CRASH | April 2016 |
| Hertfordshire | CRASH | April 2016 |
| Cambridgeshire | CRASH | May 2016 |
| Lancashire | CRASH | December 2018 |
| Sussex | CRASH | April 2019 |
| Police Scotland | CRASH | April 2019 |
| Greater Manchester | CRASH | February 2021 |
| Nottinghamshire | CRASH | February 2021 |
| West Yorkshire | CRASH | April 2021 |
| Dyfed-Powys | CRASH | June 2023 |
| Leicestershire | Other | January 2024 |
| Northamptonshire | Other | January 2024 |
| Cheshire | Other | May 2024 |
| Cleveland | Other | August 2024 |
| Derbyshire | Other | November 2024 |
| Avon and Somerset | Other | January 2025 |
| Dorset | Other | March 2025 |
| Wiltshire | CRASH | May 2025 |
| Hampshire | Other | July 2025 |
| Thames Valley Police | Other | July 2025 |
| South Wales | Other | December 2025 |
Overview of the severity adjustment method
The introduction of IBRS appears to have led to a change in the reported severity of road casualties. This can be explained by the change of reporting systems from Non-Injury-Based Reporting Systems (NIBRS), where judgement of the casualty severity is made by the reporting police officer, to IBRS, where the severity of the injury is determined automatically from the most severe type of injury suffered. It appears that some casualties that would have been categorised as ‘slight’ on NIBRS are recorded as ‘serious’ in IBRS. This became apparent from initial analysis of high level data suggesting that switching to CRASH and COPA added between 5 and 15% to the Great Britain total for ‘serious’ injuries (DfT, 2017).
The Office for National Statistics (ONS) Methodology Advisory Service have developed a methodology to quantify the effect of the introduction of injury based reporting systems (CRASH and COPA) on the number of slight and serious injuries reported to the police, and to estimate the level of slight and serious injuries as if all police forces were using injury-based reporting systems. This is described in detail in the final ONS methodology report. The final report was published alongside our 2018 statistical release to set out how this methodology was finalised.
This methodology has allowed us to produce adjusted figures for the changes in injury severity as experimental statistics. In 2018, we implemented the severity adjustment methodology for the first time and published adjusted figures in a limited number of our statistical tables. In 2019 we included adjusted figures in all of the statistical tables that were published alongside the annual report.
We also include probabilities of each casualty being serious under injury-based systems alongside the underlying dataset. Further guidance is given in the Annex to the adjustments method (PDF, 3,148KB).
In 2024, the adjusted figures were reviewed by the Office for Statistics Regulation (OSR) and designated as accredited official statistics, confirming that they comply with the standards set out in the Statistics Code of Practice.
Impact on trends
Following the introduction of CRASH and COPA, the number of casualties recorded as serious has increased in Great Britain. Chart 1 shows the number of reported serious road casualties by police force over time, from two years before to two years after injury based reporting systems were introduced (year introduced, index = 100).
Chart 1: Reported serious road casualties by police force, two years before to two years after injury based reporting systems were introduced
Chart 1 shows that the size of the increase in serious casualties varies across police forces following the introduction of injury based reporting systems. A comparison line for non-IBRS forces has been included to show how reported serious casualties have changed in these forces. Some forces (such as the Metropolitan Police Service) show a more marked increase in serious casualties than others, while other forces (such as Durham) show a more stable trend in serious casualties over time. Devon and Cornwall and South Yorkshire have also been highlighted in Chart 1 to illustrate the variety of trends observed.
The differences in the impact of the introduction of injury based reporting systems is likely to depend on the practices within a police force that were in place before these new systems were introduced. For example, Durham have stated that having a relatively low number of casualties each year allows them to extensively validate how the severity of each casualty reflects the injury received, and that their previous system for severity recording was very similar to the CRASH approach. Whereas, larger forces might not be able to carry out extensive severity reviews and there might be more differences in practices between the large numbers of officers recording accidents.
Guidance on severity adjustment use
The flow diagram in Figure 2 shows an overview on when we consider that the adjusted and unadjusted figures are most appropriate to use, though all users should carefully considered their specific circumstances and we are happy to provide more detailed advice if helpful.
Figure 2: Guidance on when to use severity adjustments
Tables 3 and 4 below provide more in-depth guidance on when to use adjusted severities depending on the geographies and time series included in the analysis.
Comparing within the same geography or police force
Table 3: Use of adjustments when comparing within an area
| Option selected | Result |
|---|---|
| Has used IBRS for the whole time period used in the analysis | No need to use adjusted severities |
| Has used IBRS for some of the time period used in the analysis | Severity adjustment needed |
| Uses IBRS but not for the time period I am examining | No need to use adjusted severities |
| Has not switched to using IBRS | No need to use adjusted severities |
Comparing across geographies or police forces
Table 4: Use of adjustments when comparing across areas
| Police force using IBRS | Time period | Result |
|---|---|---|
| All forces using injury based recording system | Whole time period is on injury based reporting system | No need to adjust, all the police forces analysed are using an injury based recording system over the time period we are analysing |
| All forces using injury based recording system | Some of the time period is on injury based recording system | Severity adjustment needed as some of the data analysed was recorded on IBRS and some was recorded on non-IBRS. There is a break in the series and comparisons are not reliable unless the adjustment is used to account for the change in the reporting system |
| All forces using injury based recording system | Whole time period in non_IBRS | No adjustment needed |
| Some forces using IBRS | Whole time period | Severity adjustment needed |
| Some forces using IBRS | Some of the time period | Severity adjustment needed |
| Some forces using IBRS | None of the time period | No severity adjustment needed |
| None of the police forces | Whole time period | No severity adjustment needed |
Robustness of the adjustments - sensitivity analysis
In police force areas where injury-based reporting systems are not used, adjusted figures are estimates of the number of serious injures that would have been recorded were an IBRS in place. These estimates depend on the model used, and different approaches may lead to different estimates. To assess the robustness of the model to the inclusion of different variables, we have carried out some sensitivity analysis.
Forces joining Injury Based Reporting Systems
In 2021, we conducted sensitivity analysis to understand how adding an extra year of data affects the severity probabilities. When comparing adjusted figures between the 2019 and 2020 models, there was less than a 0.5% change on the annual trends for all seriously injured adjusted figures. When we looked at police forces breakdowns we noticed that the level of change is different depending on the police force. There is a higher percentage change for police forces that joined an injury based reporting system (IBRS) in 2019 (2 to 8%) with the highest percentage change for Police Scotland. Police forces that joined an IBRS in 2016 and the ones which are on a non-injury based reporting system (non-IBRS) had a percentage change of less than 2%.
Merging of forces
The model was updated in 2021 for use in producing 2020 adjustments. For this model run, all Scottish police forces have been grouped together into one police force called Police Scotland. The grouping of all Scottish police forces led to a slight increase in serious injuries, but had no impact on other police forces which have an IBRS. However, it affected police forces which have a non-IBRS due to the change in median police force.
Historical revisions to casualty severity
For the 2021 model, there was a revision to historic figures for slight and serious injuries impacting data as far back as 2012. Prior to 2020, whether a casualty was reported as ‘admitted to hospital’ factored into casualty severity calculations in the CRASH system. Since 2020 this is no longer the case. Historic cases since the introduction of CRASH have been updated and corrected to reflect this change. As a result some casualty severities have been downgraded between 2012 and 2019 compared to previously published numbers. Further information is available in the background guidance.
A sensitivity check was carried out to understand the effect of revising the severities on the model. This caused a decrease of 2 to 3% in the adjusted serious casualties compared to the model run using the pre-revision severities. These severity changes affected only casualties reported by police forces that have adopted CRASH. The correction to historic casualty severities affected police force severity adjustments differently depending on their size and the number of revisions for that police force. But there was no substantive changes to trends over time.
Nevertheless, the severity revision affected Gloucestershire police force slightly differently compared to other police forces. The revision caused the historic adjusted serious time series (prior to the adoption of CRASH) to be lower than unadjusted. While unusual, this is possible with the adjustment methodology used and reflects the fact that coding of injury severity is likely to have varied across forces prior to adoption of IBRS. It may be that Gloucestershire police were already recording a higher proportion of casualties as seriously injured, relative to other forces, so that the modelled impact of moving to IBRS is different.
Removal of mobile device indicator
For the 2022 model update, we removed the variable which was used to indicate whether a force collected the data via a mobile device, as this was found to have a minimal impact on the results and removing it was found to have a very small impact on the figures. In the next few years, we also expect to update the model as further forces move to an injury based reporting system.
Data from non-CRASH forces
During 2024 and 2025, the first injury-based data from forces not using the CRASH or COPA systems has been received. In some cases, most notably for Northamptonshire, the addition of this data to the model appears to have a large impact on the model. Therefore, for the final 2024 statistics, Northamptonshire was treated as though it were not using an injury-based system, with estimates made as for other non-IBRS forces. In 2025, all forces shown in Table 2 were included within the model, resulting in a reduction of around 2% in the estimated number of serious injuries nationally, though with no material change in the trend. This change reflects the fact that forces adopting receive an estimate based on actual data from the specific force, rather than the median value. Further work, and more data for the forces which have recently adopted IBRs, is required to understand this issue further - this will be kept under regular review in future years.
Future of severity adjustments
Severity adjustments are likely to be required while forces are using a mix of injury-based and non injury-based systems. However, when all forces have adopted injury-based reporting, adjustments will not be required except for historic data (before such systems were introduced in each police force area).
As adoption of injury-based reporting systems approaches national coverage, the detailed injury severity and injury type information available through these systems is expected to become an increasingly important source of information on the outcomes of road collisions in Great Britain.
We will monitor the adoption of IBRSs as police forces implement the new STATS19 specification following the 2018 review, and provide an update in our future roadmap.
Your feedback
We welcome your feedback on this approach, specifically how you are using these statistics and whether this meets your needs. Please contact the road safety statistics team.
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